[perl5.git] / lib / Math / BigInt.pm

package Math::BigInt;

#
# "Mike had an infinite amount to do and a negative amount of time in which
# to do it." - Before and After
#

# The following hash values are used:
#   value: unsigned int with actual value (as a Math::BigInt::Calc or similiar)
#   sign : +,-,NaN,+inf,-inf
#   _a   : accuracy
#   _p   : precision
#   _f   : flags, used by MBF to flag parts of a float as untouchable

# Remember not to take shortcuts ala $xs = $x->{value}; $CALC->foo($xs); since
# underlying lib might change the reference!

my $class = "Math::BigInt";
require 5.005;

$VERSION = '1.55';
use Exporter;
@ISA =       qw( Exporter );
@EXPORT_OK = qw( objectify _swap bgcd blcm); 
use vars qw/$round_mode $accuracy $precision $div_scale $rnd_mode/;
use vars qw/$upgrade $downgrade/;
use strict;

# Inside overload, the first arg is always an object. If the original code had
# it reversed (like $x = 2 * $y), then the third paramater indicates this
# swapping. To make it work, we use a helper routine which not only reswaps the
# params, but also makes a new object in this case. See _swap() for details,
# especially the cases of operators with different classes.

# For overloaded ops with only one argument we simple use $_[0]->copy() to
# preserve the argument.

# Thus inheritance of overload operators becomes possible and transparent for
# our subclasses without the need to repeat the entire overload section there.

use overload
'='     =>      sub { $_[0]->copy(); },

# '+' and '-' do not use _swap, since it is a triffle slower. If you want to
# override _swap (if ever), then override overload of '+' and '-', too!
# for sub it is a bit tricky to keep b: b-a => -a+b
'-'	=>	sub { my $c = $_[0]->copy; $_[2] ?
                   $c->bneg()->badd($_[1]) :
                   $c->bsub( $_[1]) },
'+'	=>	sub { $_[0]->copy()->badd($_[1]); },

# some shortcuts for speed (assumes that reversed order of arguments is routed
# to normal '+' and we thus can always modify first arg. If this is changed,
# this breaks and must be adjusted.)
'+='	=>	sub { $_[0]->badd($_[1]); },
'-='	=>	sub { $_[0]->bsub($_[1]); },
'*='	=>	sub { $_[0]->bmul($_[1]); },
'/='	=>	sub { scalar $_[0]->bdiv($_[1]); },
'%='	=>	sub { $_[0]->bmod($_[1]); },
'^='	=>	sub { $_[0]->bxor($_[1]); },
'&='	=>	sub { $_[0]->band($_[1]); },
'|='	=>	sub { $_[0]->bior($_[1]); },
'**='	=>	sub { $_[0]->bpow($_[1]); },

# not supported by Perl yet
'..'	=>	\&_pointpoint,

'<=>'	=>	sub { $_[2] ?
                      ref($_[0])->bcmp($_[1],$_[0]) : 
                      ref($_[0])->bcmp($_[0],$_[1])},
'cmp'	=>	sub {
         $_[2] ? 
               "$_[1]" cmp $_[0]->bstr() :
               $_[0]->bstr() cmp "$_[1]" },

'log'	=>	sub { $_[0]->copy()->blog(); }, 
'int'	=>	sub { $_[0]->copy(); }, 
'neg'	=>	sub { $_[0]->copy()->bneg(); }, 
'abs'	=>	sub { $_[0]->copy()->babs(); },
'sqrt'  =>	sub { $_[0]->copy()->bsqrt(); },
'~'	=>	sub { $_[0]->copy()->bnot(); },

'*'	=>	sub { my @a = ref($_[0])->_swap(@_); $a[0]->bmul($a[1]); },
'/'	=>	sub { my @a = ref($_[0])->_swap(@_);scalar $a[0]->bdiv($a[1]);},
'%'	=>	sub { my @a = ref($_[0])->_swap(@_); $a[0]->bmod($a[1]); },
'**'	=>	sub { my @a = ref($_[0])->_swap(@_); $a[0]->bpow($a[1]); },
'<<'	=>	sub { my @a = ref($_[0])->_swap(@_); $a[0]->blsft($a[1]); },
'>>'	=>	sub { my @a = ref($_[0])->_swap(@_); $a[0]->brsft($a[1]); },

'&'	=>	sub { my @a = ref($_[0])->_swap(@_); $a[0]->band($a[1]); },
'|'	=>	sub { my @a = ref($_[0])->_swap(@_); $a[0]->bior($a[1]); },
'^'	=>	sub { my @a = ref($_[0])->_swap(@_); $a[0]->bxor($a[1]); },

# can modify arg of ++ and --, so avoid a new-copy for speed, but don't
# use $_[0]->__one(), it modifies $_[0] to be 1!
'++'	=>	sub { $_[0]->binc() },
'--'	=>	sub { $_[0]->bdec() },

# if overloaded, O(1) instead of O(N) and twice as fast for small numbers
'bool'  =>	sub {
  # this kludge is needed for perl prior 5.6.0 since returning 0 here fails :-/
  # v5.6.1 dumps on that: return !$_[0]->is_zero() || undef;		    :-(
  my $t = !$_[0]->is_zero();
  undef $t if $t == 0;
  $t;
  },

# the original qw() does not work with the TIESCALAR below, why?
# Order of arguments unsignificant
'""' => sub { $_[0]->bstr(); },
'0+' => sub { $_[0]->numify(); }
;

##############################################################################
# global constants, flags and accessory

use constant MB_NEVER_ROUND => 0x0001;

my $NaNOK=1; 				# are NaNs ok?
my $nan = 'NaN'; 			# constants for easier life

my $CALC = 'Math::BigInt::Calc';	# module to do low level math
my $IMPORT = 0;				# did import() yet?

$round_mode = 'even'; # one of 'even', 'odd', '+inf', '-inf', 'zero' or 'trunc'
$accuracy   = undef;
$precision  = undef;
$div_scale  = 40;

$upgrade = undef;			# default is no upgrade
$downgrade = undef;			# default is no downgrade

##############################################################################
# the old code had $rnd_mode, so we need to support it, too

$rnd_mode   = 'even';
sub TIESCALAR  { my ($class) = @_; bless \$round_mode, $class; }
sub FETCH      { return $round_mode; }
sub STORE      { $rnd_mode = $_[0]->round_mode($_[1]); }

BEGIN { tie $rnd_mode, 'Math::BigInt'; }

############################################################################## 

sub round_mode
  {
  no strict 'refs';
  # make Class->round_mode() work
  my $self = shift;
  my $class = ref($self) || $self || __PACKAGE__;
  if (defined $_[0])
    {
    my $m = shift;
    die "Unknown round mode $m"
     if $m !~ /^(even|odd|\+inf|\-inf|zero|trunc)$/;
    return ${"${class}::round_mode"} = $m;
    }
  return ${"${class}::round_mode"};
  }

sub upgrade
  {
  no strict 'refs';
  # make Class->upgrade() work
  my $self = shift;
  my $class = ref($self) || $self || __PACKAGE__;
  # need to set new value?
  if (@_ > 0)
    {
    my $u = shift;
    return ${"${class}::upgrade"} = $u;
    }
  return ${"${class}::upgrade"};
  }

sub downgrade
  {
  no strict 'refs';
  # make Class->downgrade() work
  my $self = shift;
  my $class = ref($self) || $self || __PACKAGE__;
  # need to set new value?
  if (@_ > 0)
    {
    my $u = shift;
    return ${"${class}::downgrade"} = $u;
    }
  return ${"${class}::downgrade"};
  }

sub div_scale
  {
  no strict 'refs';
  # make Class->round_mode() work
  my $self = shift;
  my $class = ref($self) || $self || __PACKAGE__;
  if (defined $_[0])
    {
    die ('div_scale must be greater than zero') if $_[0] < 0;
    ${"${class}::div_scale"} = shift;
    }
  return ${"${class}::div_scale"};
  }

sub accuracy
  {
  # $x->accuracy($a);		ref($x)	$a
  # $x->accuracy();		ref($x)
  # Class->accuracy();		class
  # Class->accuracy($a);	class $a

  my $x = shift;
  my $class = ref($x) || $x || __PACKAGE__;

  no strict 'refs';
  # need to set new value?
  if (@_ > 0)
    {
    my $a = shift;
    die ('accuracy must not be zero') if defined $a && $a == 0;
    if (ref($x))
      {
      # $object->accuracy() or fallback to global
      $x->bround($a) if defined $a;
      $x->{_a} = $a;			# set/overwrite, even if not rounded
      $x->{_p} = undef;			# clear P
      }
    else
      {
      # set global
      ${"${class}::accuracy"} = $a;
      ${"${class}::precision"} = undef;	# clear P
      }
    return $a;				# shortcut
    }

  if (ref($x))
    {
    # $object->accuracy() or fallback to global
    return $x->{_a} || ${"${class}::accuracy"};
    }
  return ${"${class}::accuracy"};
  } 

sub precision
  {
  # $x->precision($p);		ref($x)	$p
  # $x->precision();		ref($x)
  # Class->precision();		class
  # Class->precision($p);	class $p

  my $x = shift;
  my $class = ref($x) || $x || __PACKAGE__;

  no strict 'refs';
  # need to set new value?
  if (@_ > 0)
    {
    my $p = shift;
    if (ref($x))
      {
      # $object->precision() or fallback to global
      $x->bfround($p) if defined $p;
      $x->{_p} = $p;			# set/overwrite, even if not rounded
      $x->{_a} = undef;			# clear A
      }
    else
      {
      # set global
      ${"${class}::precision"} = $p;
      ${"${class}::accuracy"} = undef;	# clear A
      }
    return $p;				# shortcut
    }

  if (ref($x))
    {
    # $object->precision() or fallback to global
    return $x->{_p} || ${"${class}::precision"};
    }
  return ${"${class}::precision"};
  } 

sub config
  {
  # return (later set?) configuration data as hash ref
  my $class = shift || 'Math::BigInt';

  no strict 'refs';
  my $lib = $CALC;
  my $cfg = {
    lib => $lib,
    lib_version => ${"${lib}::VERSION"},
    class => $class,
    };
  foreach (
   qw/upgrade downgrade precision accuracy round_mode VERSION div_scale/)
    {
    $cfg->{lc($_)} = ${"${class}::$_"};
    };
  $cfg;
  }

sub _scale_a
  { 
  # select accuracy parameter based on precedence,
  # used by bround() and bfround(), may return undef for scale (means no op)
  my ($x,$s,$m,$scale,$mode) = @_;
  $scale = $x->{_a} if !defined $scale;
  $scale = $s if (!defined $scale);
  $mode = $m if !defined $mode;
  return ($scale,$mode);
  }

sub _scale_p
  { 
  # select precision parameter based on precedence,
  # used by bround() and bfround(), may return undef for scale (means no op)
  my ($x,$s,$m,$scale,$mode) = @_;
  $scale = $x->{_p} if !defined $scale;
  $scale = $s if (!defined $scale);
  $mode = $m if !defined $mode;
  return ($scale,$mode);
  }

##############################################################################
# constructors

sub copy
  {
  my ($c,$x);
  if (@_ > 1)
    {
    # if two arguments, the first one is the class to "swallow" subclasses
    ($c,$x) = @_;
    }
  else
    {
    $x = shift;
    $c = ref($x);
    }
  return unless ref($x); # only for objects

  my $self = {}; bless $self,$c;
  my $r;
  foreach my $k (keys %$x)
    {
    if ($k eq 'value')
      {
      $self->{value} = $CALC->_copy($x->{value}); next;
      }
    if (!($r = ref($x->{$k})))
      {
      $self->{$k} = $x->{$k}; next;
      }
    if ($r eq 'SCALAR')
      {
      $self->{$k} = \${$x->{$k}};
      }
    elsif ($r eq 'ARRAY')
      {
      $self->{$k} = [ @{$x->{$k}} ];
      }
    elsif ($r eq 'HASH')
      {
      # only one level deep!
      foreach my $h (keys %{$x->{$k}})
        {
        $self->{$k}->{$h} = $x->{$k}->{$h};
        }
      }
    else # normal ref
      {
      my $xk = $x->{$k};
      if ($xk->can('copy'))
        {
	$self->{$k} = $xk->copy();
        }
      else
	{
	$self->{$k} = $xk->new($xk);
	}
      }
    }
  $self;
  }

sub new 
  {
  # create a new BigInt object from a string or another BigInt object. 
  # see hash keys documented at top

  # the argument could be an object, so avoid ||, && etc on it, this would
  # cause costly overloaded code to be called. The only allowed ops are
  # ref() and defined.

  my ($class,$wanted,$a,$p,$r) = @_;
 
  # avoid numify-calls by not using || on $wanted!
  return $class->bzero($a,$p) if !defined $wanted;	# default to 0
  return $class->copy($wanted,$a,$p,$r)
   if ref($wanted) && $wanted->isa($class);		# MBI or subclass

  $class->import() if $IMPORT == 0;		# make require work
  
  my $self = bless {}, $class;

  # shortcut for "normal" numbers
  if ((!ref $wanted) && ($wanted =~ /^([+-]?)[1-9][0-9]*$/))
    {
    $self->{sign} = $1 || '+';
    my $ref = \$wanted;
    if ($wanted =~ /^[+-]/)
     {
      # remove sign without touching wanted
      my $t = $wanted; $t =~ s/^[+-]//; $ref = \$t;
      }
    $self->{value} = $CALC->_new($ref);
    no strict 'refs';
    if ( (defined $a) || (defined $p) 
        || (defined ${"${class}::precision"})
        || (defined ${"${class}::accuracy"}) 
       )
      {
      $self->round($a,$p,$r) unless (@_ == 4 && !defined $a && !defined $p);
      }
    return $self;
    }

  # handle '+inf', '-inf' first
  if ($wanted =~ /^[+-]?inf$/)
    {
    $self->{value} = $CALC->_zero();
    $self->{sign} = $wanted; $self->{sign} = '+inf' if $self->{sign} eq 'inf';
    return $self;
    }
  # split str in m mantissa, e exponent, i integer, f fraction, v value, s sign
  my ($mis,$miv,$mfv,$es,$ev) = _split(\$wanted);
  if (!ref $mis)
    {
    die "$wanted is not a number initialized to $class" if !$NaNOK;
    #print "NaN 1\n";
    $self->{value} = $CALC->_zero();
    $self->{sign} = $nan;
    return $self;
    }
  if (!ref $miv)
    {
    # _from_hex or _from_bin
    $self->{value} = $mis->{value};
    $self->{sign} = $mis->{sign};
    return $self;	# throw away $mis
    }
  # make integer from mantissa by adjusting exp, then convert to bigint
  $self->{sign} = $$mis;			# store sign
  $self->{value} = $CALC->_zero();		# for all the NaN cases
  my $e = int("$$es$$ev");			# exponent (avoid recursion)
  if ($e > 0)
    {
    my $diff = $e - CORE::length($$mfv);
    if ($diff < 0)				# Not integer
      {
      #print "NOI 1\n";
      return $upgrade->new($wanted,$a,$p,$r) if defined $upgrade;
      $self->{sign} = $nan;
      }
    else					# diff >= 0
      {
      # adjust fraction and add it to value
      # print "diff > 0 $$miv\n";
      $$miv = $$miv . ($$mfv . '0' x $diff);
      }
    }
  else
    {
    if ($$mfv ne '')				# e <= 0
      {
      # fraction and negative/zero E => NOI
      #print "NOI 2 \$\$mfv '$$mfv'\n";
      return $upgrade->new($wanted,$a,$p,$r) if defined $upgrade;
      $self->{sign} = $nan;
      }
    elsif ($e < 0)
      {
      # xE-y, and empty mfv
      #print "xE-y\n";
      $e = abs($e);
      if ($$miv !~ s/0{$e}$//)		# can strip so many zero's?
        {
        #print "NOI 3\n";
        return $upgrade->new($wanted,$a,$p,$r) if defined $upgrade;
        $self->{sign} = $nan;
        }
      }
    }
  $self->{sign} = '+' if $$miv eq '0';			# normalize -0 => +0
  $self->{value} = $CALC->_new($miv) if $self->{sign} =~ /^[+-]$/;
  # if any of the globals is set, use them to round and store them inside $self
  # do not round for new($x,undef,undef) since that is used by MBF to signal
  # no rounding
  $self->round($a,$p,$r) unless @_ == 4 && !defined $a && !defined $p;
  $self;
  }

sub bnan
  {
  # create a bigint 'NaN', if given a BigInt, set it to 'NaN'
  my $self = shift;
  $self = $class if !defined $self;
  if (!ref($self))
    {
    my $c = $self; $self = {}; bless $self, $c;
    }
  $self->import() if $IMPORT == 0;		# make require work
  return if $self->modify('bnan');
  my $c = ref($self);
  if ($self->can('_bnan'))
    {
    # use subclass to initialize
    $self->_bnan();
    }
  else
    {
    # otherwise do our own thing
    $self->{value} = $CALC->_zero();
    }
  $self->{value} = $CALC->_zero();
  $self->{sign} = $nan;
  delete $self->{_a}; delete $self->{_p};	# rounding NaN is silly
  return $self;
  }

sub binf
  {
  # create a bigint '+-inf', if given a BigInt, set it to '+-inf'
  # the sign is either '+', or if given, used from there
  my $self = shift;
  my $sign = shift; $sign = '+' if !defined $sign || $sign !~ /^-(inf)?$/;
  $self = $class if !defined $self;
  if (!ref($self))
    {
    my $c = $self; $self = {}; bless $self, $c;
    }
  $self->import() if $IMPORT == 0;		# make require work
  return if $self->modify('binf');
  my $c = ref($self);
  if ($self->can('_binf'))
    {
    # use subclass to initialize
    $self->_binf();
    }
  else
    {
    # otherwise do our own thing
    $self->{value} = $CALC->_zero();
    }
  $sign = $sign . 'inf' if $sign !~ /inf$/;	# - => -inf
  $self->{sign} = $sign;
  ($self->{_a},$self->{_p}) = @_;		# take over requested rounding
  return $self;
  }

sub bzero
  {
  # create a bigint '+0', if given a BigInt, set it to 0
  my $self = shift;
  $self = $class if !defined $self;
 
  if (!ref($self))
    {
    my $c = $self; $self = {}; bless $self, $c;
    }
  $self->import() if $IMPORT == 0;		# make require work
  return if $self->modify('bzero');

  if ($self->can('_bzero'))
    {
    # use subclass to initialize
    $self->_bzero();
    }
  else
    {
    # otherwise do our own thing
    $self->{value} = $CALC->_zero();
    }
  $self->{sign} = '+';
  if (@_ > 0)
    {
    $self->{_a} = $_[0]
     if (defined $self->{_a} && defined $_[0] && $_[0] > $self->{_a});
    $self->{_p} = $_[1]
     if (defined $self->{_p} && defined $_[1] && $_[1] < $self->{_p});
    }
  return $self;
  }

sub bone
  {
  # create a bigint '+1' (or -1 if given sign '-'),
  # if given a BigInt, set it to +1 or -1, respecively
  my $self = shift;
  my $sign = shift; $sign = '+' if !defined $sign || $sign ne '-';
  $self = $class if !defined $self;
  
  if (!ref($self))
    {
    my $c = $self; $self = {}; bless $self, $c;
    }
  $self->import() if $IMPORT == 0;		# make require work
  return if $self->modify('bone');

  if ($self->can('_bone'))
    {
    # use subclass to initialize
    $self->_bone();
    }
  else
    {
    # otherwise do our own thing
    $self->{value} = $CALC->_one();
    }
  $self->{sign} = $sign;
  if (@_ > 0)
    {
    $self->{_a} = $_[0]
     if (defined $self->{_a} && defined $_[0] && $_[0] > $self->{_a});
    $self->{_p} = $_[1]
     if (defined $self->{_p} && defined $_[1] && $_[1] < $self->{_p});
    }
  return $self;
  }

##############################################################################
# string conversation

sub bsstr
  {
  # (ref to BFLOAT or num_str ) return num_str
  # Convert number from internal format to scientific string format.
  # internal format is always normalized (no leading zeros, "-0E0" => "+0E0")
  my $x = shift; $class = ref($x) || $x; $x = $class->new(shift) if !ref($x); 
  # my ($self,$x) = ref($_[0]) ? (ref($_[0]),$_[0]) : objectify(1,@_); 

  if ($x->{sign} !~ /^[+-]$/)
    {
    return $x->{sign} unless $x->{sign} eq '+inf';	# -inf, NaN
    return 'inf';					# +inf
    }
  my ($m,$e) = $x->parts();
  # e can only be positive
  my $sign = 'e+';	
  # MBF: my $s = $e->{sign}; $s = '' if $s eq '-'; my $sep = 'e'.$s;
  return $m->bstr().$sign.$e->bstr();
  }

sub bstr 
  {
  # make a string from bigint object
  my $x = shift; $class = ref($x) || $x; $x = $class->new(shift) if !ref($x); 
  # my ($self,$x) = ref($_[0]) ? (ref($_[0]),$_[0]) : objectify(1,@_); 

  if ($x->{sign} !~ /^[+-]$/)
    {
    return $x->{sign} unless $x->{sign} eq '+inf';	# -inf, NaN
    return 'inf';					# +inf
    }
  my $es = ''; $es = $x->{sign} if $x->{sign} eq '-';
  return $es.${$CALC->_str($x->{value})};
  }

sub numify 
  {
  # Make a "normal" scalar from a BigInt object
  my $x = shift; $x = $class->new($x) unless ref $x;
  return $x->{sign} if $x->{sign} !~ /^[+-]$/;
  my $num = $CALC->_num($x->{value});
  return -$num if $x->{sign} eq '-';
  $num;
  }

##############################################################################
# public stuff (usually prefixed with "b")

sub sign
  {
  # return the sign of the number: +/-/-inf/+inf/NaN
  my ($self,$x) = ref($_[0]) ? (ref($_[0]),$_[0]) : objectify(1,@_); 
  
  $x->{sign};
  }

sub _find_round_parameters
  {
  # After any operation or when calling round(), the result is rounded by
  # regarding the A & P from arguments, local parameters, or globals.

  # This procedure finds the round parameters, but it is for speed reasons
  # duplicated in round. Otherwise, it is tested by the testsuite and used
  # by fdiv().
  
  my ($self,$a,$p,$r,@args) = @_;
  # $a accuracy, if given by caller
  # $p precision, if given by caller
  # $r round_mode, if given by caller
  # @args all 'other' arguments (0 for unary, 1 for binary ops)

  # leave bigfloat parts alone
  return ($self) if exists $self->{_f} && $self->{_f} & MB_NEVER_ROUND != 0;

  my $c = ref($self);				# find out class of argument(s)
  no strict 'refs';

  # now pick $a or $p, but only if we have got "arguments"
  if (!defined $a)
    {
    foreach ($self,@args)
      {
      # take the defined one, or if both defined, the one that is smaller
      $a = $_->{_a} if (defined $_->{_a}) && (!defined $a || $_->{_a} < $a);
      }
    }
  if (!defined $p)
    {
    # even if $a is defined, take $p, to signal error for both defined
    foreach ($self,@args)
      {
      # take the defined one, or if both defined, the one that is bigger
      # -2 > -3, and 3 > 2
      $p = $_->{_p} if (defined $_->{_p}) && (!defined $p || $_->{_p} > $p);
      }
    }
  # if still none defined, use globals (#2)
  $a = ${"$c\::accuracy"} unless defined $a;
  $p = ${"$c\::precision"} unless defined $p;
 
  # no rounding today? 
  return ($self) unless defined $a || defined $p;		# early out

  # set A and set P is an fatal error
  return ($self->bnan()) if defined $a && defined $p;

  $r = ${"$c\::round_mode"} unless defined $r;
  die "Unknown round mode '$r'" if $r !~ /^(even|odd|\+inf|\-inf|zero|trunc)$/;
 
  return ($self,$a,$p,$r);
  }

sub round
  {
  # Round $self according to given parameters, or given second argument's
  # parameters or global defaults 

  # for speed reasons, _find_round_parameters is embeded here:

  my ($self,$a,$p,$r,@args) = @_;
  # $a accuracy, if given by caller
  # $p precision, if given by caller
  # $r round_mode, if given by caller
  # @args all 'other' arguments (0 for unary, 1 for binary ops)

  # leave bigfloat parts alone
  return ($self) if exists $self->{_f} && $self->{_f} & MB_NEVER_ROUND != 0;

  my $c = ref($self);				# find out class of argument(s)
  no strict 'refs';

  # now pick $a or $p, but only if we have got "arguments"
  if (!defined $a)
    {
    foreach ($self,@args)
      {
      # take the defined one, or if both defined, the one that is smaller
      $a = $_->{_a} if (defined $_->{_a}) && (!defined $a || $_->{_a} < $a);
      }
    }
  if (!defined $p)
    {
    # even if $a is defined, take $p, to signal error for both defined
    foreach ($self,@args)
      {
      # take the defined one, or if both defined, the one that is bigger
      # -2 > -3, and 3 > 2
      $p = $_->{_p} if (defined $_->{_p}) && (!defined $p || $_->{_p} > $p);
      }
    }
  # if still none defined, use globals (#2)
  $a = ${"$c\::accuracy"} unless defined $a;
  $p = ${"$c\::precision"} unless defined $p;
 
  # no rounding today? 
  return $self unless defined $a || defined $p;		# early out

  # set A and set P is an fatal error
  return $self->bnan() if defined $a && defined $p;

  $r = ${"$c\::round_mode"} unless defined $r;
  die "Unknown round mode '$r'" if $r !~ /^(even|odd|\+inf|\-inf|zero|trunc)$/;

  # now round, by calling either fround or ffround:
  if (defined $a)
    {
    $self->bround($a,$r) if !defined $self->{_a} || $self->{_a} >= $a;
    }
  else # both can't be undefined due to early out
    {
    $self->bfround($p,$r) if !defined $self->{_p} || $self->{_p} <= $p;
    }
  $self->bnorm();			# after round, normalize
  }

sub bnorm
  { 
  # (numstr or BINT) return BINT
  # Normalize number -- no-op here
  my ($self,$x) = ref($_[0]) ? (ref($_[0]),$_[0]) : objectify(1,@_);
  $x;
  }

sub babs 
  {
  # (BINT or num_str) return BINT
  # make number absolute, or return absolute BINT from string
  my ($self,$x) = ref($_[0]) ? (ref($_[0]),$_[0]) : objectify(1,@_);

  return $x if $x->modify('babs');
  # post-normalized abs for internal use (does nothing for NaN)
  $x->{sign} =~ s/^-/+/;
  $x;
  }

sub bneg 
  { 
  # (BINT or num_str) return BINT
  # negate number or make a negated number from string
  my ($self,$x) = ref($_[0]) ? (ref($_[0]),$_[0]) : objectify(1,@_);
  
  return $x if $x->modify('bneg');

  # for +0 dont negate (to have always normalized)
  $x->{sign} =~ tr/+-/-+/ if !$x->is_zero();	# does nothing for NaN
  $x;
  }

sub bcmp 
  {
  # Compares 2 values.  Returns one of undef, <0, =0, >0. (suitable for sort)
  # (BINT or num_str, BINT or num_str) return cond_code
  my ($self,$x,$y) = objectify(2,@_);

  if (($x->{sign} !~ /^[+-]$/) || ($y->{sign} !~ /^[+-]$/))
    {
    # handle +-inf and NaN
    return undef if (($x->{sign} eq $nan) || ($y->{sign} eq $nan));
    return 0 if $x->{sign} eq $y->{sign} && $x->{sign} =~ /^[+-]inf$/;
    return +1 if $x->{sign} eq '+inf';
    return -1 if $x->{sign} eq '-inf';
    return -1 if $y->{sign} eq '+inf';
    return +1;
    }
  # check sign for speed first
  return 1 if $x->{sign} eq '+' && $y->{sign} eq '-';	# does also 0 <=> -y
  return -1 if $x->{sign} eq '-' && $y->{sign} eq '+';  # does also -x <=> 0 

  # shortcut
  my $xz = $x->is_zero();
  my $yz = $y->is_zero();
  return 0 if $xz && $yz;                               # 0 <=> 0
  return -1 if $xz && $y->{sign} eq '+';                # 0 <=> +y
  return 1 if $yz && $x->{sign} eq '+';                 # +x <=> 0
  
  # post-normalized compare for internal use (honors signs)
  if ($x->{sign} eq '+') 
    {
    # $x and $y both > 0
    return $CALC->_acmp($x->{value},$y->{value});
    }

  # $x && $y both < 0
  $CALC->_acmp($y->{value},$x->{value});	# swaped (lib does only 0,1,-1)
  }

sub bacmp 
  {
  # Compares 2 values, ignoring their signs. 
  # Returns one of undef, <0, =0, >0. (suitable for sort)
  # (BINT, BINT) return cond_code
  my ($self,$x,$y) = objectify(2,@_);
  
  if (($x->{sign} !~ /^[+-]$/) || ($y->{sign} !~ /^[+-]$/))
    {
    # handle +-inf and NaN
    return undef if (($x->{sign} eq $nan) || ($y->{sign} eq $nan));
    return 0 if $x->{sign} =~ /^[+-]inf$/ && $y->{sign} =~ /^[+-]inf$/;
    return +1;	# inf is always bigger
    }
  $CALC->_acmp($x->{value},$y->{value});	# lib does only 0,1,-1
  }

sub badd 
  {
  # add second arg (BINT or string) to first (BINT) (modifies first)
  # return result as BINT
  my ($self,$x,$y,@r) = objectify(2,@_);

  return $x if $x->modify('badd');
#  print "mbi badd ",join(' ',caller()),"\n";
#  print "upgrade => ",$upgrade||'undef',
#    " \$x (",ref($x),") \$y (",ref($y),")\n";
  return $upgrade->badd($x,$y,@r) if defined $upgrade &&
    ((ref($x) eq $upgrade) || (ref($y) eq $upgrade));
#  print "still badd\n";

  $r[3] = $y;				# no push!
  # inf and NaN handling
  if (($x->{sign} !~ /^[+-]$/) || ($y->{sign} !~ /^[+-]$/))
    {
    # NaN first
    return $x->bnan() if (($x->{sign} eq $nan) || ($y->{sign} eq $nan));
    # inf handling
    if (($x->{sign} =~ /^[+-]inf$/) && ($y->{sign} =~ /^[+-]inf$/))
      {
      # +inf++inf or -inf+-inf => same, rest is NaN
      return $x if $x->{sign} eq $y->{sign};
      return $x->bnan();
      }
    # +-inf + something => +inf
    # something +-inf => +-inf
    $x->{sign} = $y->{sign}, return $x if $y->{sign} =~ /^[+-]inf$/;
    return $x;
    }
    
  my ($sx, $sy) = ( $x->{sign}, $y->{sign} ); # get signs

  if ($sx eq $sy)  
    {
    $x->{value} = $CALC->_add($x->{value},$y->{value});	# same sign, abs add
    $x->{sign} = $sx;
    }
  else 
    {
    my $a = $CALC->_acmp ($y->{value},$x->{value});	# absolute compare
    if ($a > 0)                           
      {
      #print "swapped sub (a=$a)\n";
      $x->{value} = $CALC->_sub($y->{value},$x->{value},1); # abs sub w/ swap
      $x->{sign} = $sy;
      } 
    elsif ($a == 0)
      {
      # speedup, if equal, set result to 0
      #print "equal sub, result = 0\n";
      $x->{value} = $CALC->_zero();
      $x->{sign} = '+';
      }
    else # a < 0
      {
      #print "unswapped sub (a=$a)\n";
      $x->{value} = $CALC->_sub($x->{value}, $y->{value}); # abs sub
      $x->{sign} = $sx;
      }
    }
  $x->round(@r);
  }

sub bsub 
  {
  # (BINT or num_str, BINT or num_str) return num_str
  # subtract second arg from first, modify first
  my ($self,$x,$y,@r) = objectify(2,@_);

  return $x if $x->modify('bsub');
#  return $upgrade->badd($x,$y,@r) if defined $upgrade &&
#    ((ref($x) eq $upgrade) || (ref($y) eq $upgrade));

  if ($y->is_zero())
    { 
    return $x->round(@r);
    }

  $y->{sign} =~ tr/+\-/-+/; 	# does nothing for NaN
  $x->badd($y,@r); 		# badd does not leave internal zeros
  $y->{sign} =~ tr/+\-/-+/; 	# refix $y (does nothing for NaN)
  $x;				# already rounded by badd() or no round necc.
  }

sub binc
  {
  # increment arg by one
  my ($self,$x,$a,$p,$r) = ref($_[0]) ? (ref($_[0]),@_) : objectify(1,@_);
  return $x if $x->modify('binc');

  if ($x->{sign} eq '+')
    {
    $x->{value} = $CALC->_inc($x->{value});
    return $x->round($a,$p,$r);
    }
  elsif ($x->{sign} eq '-')
    {
    $x->{value} = $CALC->_dec($x->{value});
    $x->{sign} = '+' if $CALC->_is_zero($x->{value}); # -1 +1 => -0 => +0
    return $x->round($a,$p,$r);
    }
  # inf, nan handling etc
  $x->badd($self->__one(),$a,$p,$r);		# badd does round
  }

sub bdec
  {
  # decrement arg by one
  my ($self,$x,$a,$p,$r) = ref($_[0]) ? (ref($_[0]),@_) : objectify(1,@_);
  return $x if $x->modify('bdec');
  
  my $zero = $CALC->_is_zero($x->{value}) && $x->{sign} eq '+';
  # <= 0
  if (($x->{sign} eq '-') || $zero) 
    {
    $x->{value} = $CALC->_inc($x->{value});
    $x->{sign} = '-' if $zero;			# 0 => 1 => -1
    $x->{sign} = '+' if $CALC->_is_zero($x->{value}); # -1 +1 => -0 => +0
    return $x->round($a,$p,$r);
    }
  # > 0
  elsif ($x->{sign} eq '+')
    {
    $x->{value} = $CALC->_dec($x->{value});
    return $x->round($a,$p,$r);
    }
  # inf, nan handling etc
  $x->badd($self->__one('-'),$a,$p,$r);			# badd does round
  } 

sub blog
  {
  # not implemented yet
  my ($self,$x,$base,$a,$p,$r) = ref($_[0]) ? (ref($_[0]),@_) : objectify(1,@_);
 
  return $upgrade->blog($x,$base,$a,$p,$r) if defined $upgrade;

  return $x->bnan();
  }
 
sub blcm 
  { 
  # (BINT or num_str, BINT or num_str) return BINT
  # does not modify arguments, but returns new object
  # Lowest Common Multiplicator

  my $y = shift; my ($x);
  if (ref($y))
    {
    $x = $y->copy();
    }
  else
    {
    $x = $class->new($y);
    }
  while (@_) { $x = __lcm($x,shift); } 
  $x;
  }

sub bgcd 
  { 
  # (BINT or num_str, BINT or num_str) return BINT
  # does not modify arguments, but returns new object
  # GCD -- Euclids algorithm, variant C (Knuth Vol 3, pg 341 ff)

  my $y = shift;
  $y = __PACKAGE__->new($y) if !ref($y);
  my $self = ref($y);
  my $x = $y->copy();		# keep arguments
  if ($CALC->can('_gcd'))
    {
    while (@_)
      {
      $y = shift; $y = $self->new($y) if !ref($y);
      next if $y->is_zero();
      return $x->bnan() if $y->{sign} !~ /^[+-]$/;	# y NaN?
      $x->{value} = $CALC->_gcd($x->{value},$y->{value}); last if $x->is_one();
      }
    }
  else
    {
    while (@_)
      {
      $y = shift; $y = $self->new($y) if !ref($y);
      $x = __gcd($x,$y->copy()); last if $x->is_one();	# _gcd handles NaN
      } 
    }
  $x->babs();
  }

sub bnot 
  {
  # (num_str or BINT) return BINT
  # represent ~x as twos-complement number
  # we don't need $self, so undef instead of ref($_[0]) make it slightly faster
  my ($self,$x,$a,$p,$r) = ref($_[0]) ? (undef,@_) : objectify(1,@_);
 
  return $x if $x->modify('bnot');
  $x->bneg()->bdec();			# bdec already does round
  }

# is_foo test routines

sub is_zero
  {
  # return true if arg (BINT or num_str) is zero (array '+', '0')
  # we don't need $self, so undef instead of ref($_[0]) make it slightly faster
  my ($self,$x) = ref($_[0]) ? (undef,$_[0]) : objectify(1,@_);
  
  return 0 if $x->{sign} !~ /^\+$/;			# -, NaN & +-inf aren't
  $CALC->_is_zero($x->{value});
  }

sub is_nan
  {
  # return true if arg (BINT or num_str) is NaN
  my ($self,$x) = ref($_[0]) ? (ref($_[0]),$_[0]) : objectify(1,@_);

  return 1 if $x->{sign} eq $nan;
  0;
  }

sub is_inf
  {
  # return true if arg (BINT or num_str) is +-inf
  my ($self,$x,$sign) = ref($_[0]) ? (ref($_[0]),@_) : objectify(1,@_);

  $sign = '' if !defined $sign;
  return 1 if $sign eq $x->{sign};		# match ("+inf" eq "+inf")
  return 0 if $sign !~ /^([+-]|)$/;

  if ($sign eq '')
    {
    return 1 if ($x->{sign} =~ /^[+-]inf$/); 
    return 0;
    }
  $sign = quotemeta($sign.'inf');
  return 1 if ($x->{sign} =~ /^$sign$/);
  0;
  }

sub is_one
  {
  # return true if arg (BINT or num_str) is +1
  # or -1 if sign is given
  # we don't need $self, so undef instead of ref($_[0]) make it slightly faster
  my ($self,$x,$sign) = ref($_[0]) ? (undef,@_) : objectify(1,@_);
    
  $sign = '' if !defined $sign; $sign = '+' if $sign ne '-';
 
  return 0 if $x->{sign} ne $sign; 	# -1 != +1, NaN, +-inf aren't either
  $CALC->_is_one($x->{value});
  }

sub is_odd
  {
  # return true when arg (BINT or num_str) is odd, false for even
  # we don't need $self, so undef instead of ref($_[0]) make it slightly faster
  my ($self,$x) = ref($_[0]) ? (undef,$_[0]) : objectify(1,@_);

  return 0 if $x->{sign} !~ /^[+-]$/;			# NaN & +-inf aren't
  $CALC->_is_odd($x->{value});
  }

sub is_even
  {
  # return true when arg (BINT or num_str) is even, false for odd
  # we don't need $self, so undef instead of ref($_[0]) make it slightly faster
  my ($self,$x) = ref($_[0]) ? (undef,$_[0]) : objectify(1,@_);

  return 0 if $x->{sign} !~ /^[+-]$/;			# NaN & +-inf aren't
  $CALC->_is_even($x->{value});
  }

sub is_positive
  {
  # return true when arg (BINT or num_str) is positive (>= 0)
  # we don't need $self, so undef instead of ref($_[0]) make it slightly faster
  my ($self,$x) = ref($_[0]) ? (undef,$_[0]) : objectify(1,@_);
  
  return 1 if $x->{sign} =~ /^\+/;
  0;
  }

sub is_negative
  {
  # return true when arg (BINT or num_str) is negative (< 0)
  # we don't need $self, so undef instead of ref($_[0]) make it slightly faster
  my ($self,$x) = ref($_[0]) ? (undef,$_[0]) : objectify(1,@_);
  
  return 1 if ($x->{sign} =~ /^-/);
  0;
  }

sub is_int
  {
  # return true when arg (BINT or num_str) is an integer
  # always true for BigInt, but different for Floats
  # we don't need $self, so undef instead of ref($_[0]) make it slightly faster
  my ($self,$x) = ref($_[0]) ? (undef,$_[0]) : objectify(1,@_);
  
  $x->{sign} =~ /^[+-]$/ ? 1 : 0;		# inf/-inf/NaN aren't
  }

###############################################################################

sub bmul 
  { 
  # multiply two numbers -- stolen from Knuth Vol 2 pg 233
  # (BINT or num_str, BINT or num_str) return BINT
  my ($self,$x,$y,@r) = objectify(2,@_);
  
  return $x if $x->modify('bmul');

  return $x->bnan() if (($x->{sign} eq $nan) || ($y->{sign} eq $nan));

  # inf handling
  if (($x->{sign} =~ /^[+-]inf$/) || ($y->{sign} =~ /^[+-]inf$/))
    {
    return $x->bnan() if $x->is_zero() || $y->is_zero();
    # result will always be +-inf:
    # +inf * +/+inf => +inf, -inf * -/-inf => +inf
    # +inf * -/-inf => -inf, -inf * +/+inf => -inf
    return $x->binf() if ($x->{sign} =~ /^\+/ && $y->{sign} =~ /^\+/); 
    return $x->binf() if ($x->{sign} =~ /^-/ && $y->{sign} =~ /^-/); 
    return $x->binf('-');
    }
  
  return $upgrade->bmul($x,$y,@r)
   if defined $upgrade && $y->isa($upgrade);
  
  $r[3] = $y;				# no push here

  $x->{sign} = $x->{sign} eq $y->{sign} ? '+' : '-'; # +1 * +1 or -1 * -1 => +

  $x->{value} = $CALC->_mul($x->{value},$y->{value});	# do actual math
  $x->{sign} = '+' if $CALC->_is_zero($x->{value}); 	# no -0
  $x->round(@r);
  }

sub _div_inf
  {
  # helper function that handles +-inf cases for bdiv()/bmod() to reuse code
  my ($self,$x,$y) = @_;

  # NaN if x == NaN or y == NaN or x==y==0
  return wantarray ? ($x->bnan(),$self->bnan()) : $x->bnan()
   if (($x->is_nan() || $y->is_nan())   ||
       ($x->is_zero() && $y->is_zero()));
 
  # +-inf / +-inf == NaN, reminder also NaN
  if (($x->{sign} =~ /^[+-]inf$/) && ($y->{sign} =~ /^[+-]inf$/))
    {
    return wantarray ? ($x->bnan(),$self->bnan()) : $x->bnan();
    }
  # x / +-inf => 0, remainder x (works even if x == 0)
  if ($y->{sign} =~ /^[+-]inf$/)
    {
    my $t = $x->copy();		# binf clobbers up $x
    return wantarray ? ($x->bzero(),$t) : $x->bzero()
    }
  
  # 5 / 0 => +inf, -6 / 0 => -inf
  # +inf / 0 = inf, inf,  and -inf / 0 => -inf, -inf 
  # exception:   -8 / 0 has remainder -8, not 8
  # exception: -inf / 0 has remainder -inf, not inf
  if ($y->is_zero())
    {
    # +-inf / 0 => special case for -inf
    return wantarray ?  ($x,$x->copy()) : $x if $x->is_inf();
    if (!$x->is_zero() && !$x->is_inf())
      {
      my $t = $x->copy();		# binf clobbers up $x
      return wantarray ?
       ($x->binf($x->{sign}),$t) : $x->binf($x->{sign})
      }
    }
  
  # last case: +-inf / ordinary number
  my $sign = '+inf';
  $sign = '-inf' if substr($x->{sign},0,1) ne $y->{sign};
  $x->{sign} = $sign;
  return wantarray ? ($x,$self->bzero()) : $x;
  }

sub bdiv 
  {
  # (dividend: BINT or num_str, divisor: BINT or num_str) return 
  # (BINT,BINT) (quo,rem) or BINT (only rem)
  my ($self,$x,$y,@r) = objectify(2,@_);

  return $x if $x->modify('bdiv');

  return $self->_div_inf($x,$y)
   if (($x->{sign} !~ /^[+-]$/) || ($y->{sign} !~ /^[+-]$/) || $y->is_zero());

  return $upgrade->bdiv($upgrade->new($x),$y,@r)
   if defined $upgrade && $y->isa($upgrade);

  $r[3] = $y;					# no push!

  # 0 / something
  return
   wantarray ? ($x->round(@r),$self->bzero(@r)):$x->round(@r) if $x->is_zero();
 
  # Is $x in the interval [0, $y) (aka $x <= $y) ?
  my $cmp = $CALC->_acmp($x->{value},$y->{value});
  if (($cmp < 0) and (($x->{sign} eq $y->{sign}) or !wantarray))
    {
    return $upgrade->bdiv($upgrade->new($x),$upgrade->new($y),@r)
     if defined $upgrade;

    return $x->bzero()->round(@r) unless wantarray;
    my $t = $x->copy();      # make copy first, because $x->bzero() clobbers $x
    return ($x->bzero()->round(@r),$t);
    }
  elsif ($cmp == 0)
    {
    # shortcut, both are the same, so set to +/- 1
    $x->__one( ($x->{sign} ne $y->{sign} ? '-' : '+') ); 
    return $x unless wantarray;
    return ($x->round(@r),$self->bzero(@r));
    }
  return $upgrade->bdiv($upgrade->new($x),$upgrade->new($y),@r)
   if defined $upgrade;
   
  # calc new sign and in case $y == +/- 1, return $x
  my $xsign = $x->{sign};				# keep
  $x->{sign} = ($x->{sign} ne $y->{sign} ? '-' : '+'); 
  # check for / +-1 (cant use $y->is_one due to '-'
  if ($CALC->_is_one($y->{value}))
    {
    return wantarray ? ($x->round(@r),$self->bzero(@r)) : $x->round(@r); 
    }

  if (wantarray)
    {
    my $rem = $self->bzero(); 
    ($x->{value},$rem->{value}) = $CALC->_div($x->{value},$y->{value});
    $x->{sign} = '+' if $CALC->_is_zero($x->{value});
    $x->round(@r); 
    if (! $CALC->_is_zero($rem->{value}))
      {
      $rem->{sign} = $y->{sign};
      $rem = $y-$rem if $xsign ne $y->{sign};	# one of them '-'
      }
    else
      {
      $rem->{sign} = '+';			# dont leave -0
      }
    $rem->round(@r);
    return ($x,$rem);
    }

  $x->{value} = $CALC->_div($x->{value},$y->{value});
  $x->{sign} = '+' if $CALC->_is_zero($x->{value});
  $x->round(@r); 
  }

sub bmod 
  {
  # modulus (or remainder)
  # (BINT or num_str, BINT or num_str) return BINT
  my ($self,$x,$y,@r) = objectify(2,@_);

  return $x if $x->modify('bmod');
  $r[3] = $y;					# no push!
  if (($x->{sign} !~ /^[+-]$/) || ($y->{sign} !~ /^[+-]$/) || $y->is_zero())
    {
    my ($d,$r) = $self->_div_inf($x,$y);
    return $r->round(@r);
    }

  if ($CALC->can('_mod'))
    {
    # calc new sign and in case $y == +/- 1, return $x
    $x->{value} = $CALC->_mod($x->{value},$y->{value});
    if (!$CALC->_is_zero($x->{value}))
      {
      my $xsign = $x->{sign};
      $x->{sign} = $y->{sign};
      $x = $y-$x if $xsign ne $y->{sign};	# one of them '-'
      }
    else
      {
      $x->{sign} = '+';				# dont leave -0
      }
    return $x->round(@r);
    }
  my ($t,$rem) = $self->bdiv($x->copy(),$y,@r);	# slow way (also rounds)
  # modify in place
  foreach (qw/value sign _a _p/)
    {
    $x->{$_} = $rem->{$_};
    }
  $x;
  }

sub bfac
  {
  # (BINT or num_str, BINT or num_str) return BINT
  # compute factorial numbers
  # modifies first argument
  my ($self,$x,@r) = objectify(1,@_);

  return $x if $x->modify('bfac');
 
  return $x->bnan() if $x->{sign} ne '+';	# inf, NnN, <0 etc => NaN
  return $x->bone(@r) if $x->is_zero() || $x->is_one();		# 0 or 1 => 1

  if ($CALC->can('_fac'))
    {
    $x->{value} = $CALC->_fac($x->{value});
    return $x->round(@r);
    }

  my $n = $x->copy();
  $x->bone();
  my $f = $self->new(2);
  while ($f->bacmp($n) < 0)
    {
    $x->bmul($f); $f->binc();
    }
  $x->bmul($f);					# last step
  $x->round(@r);				# round
  }
 
sub bpow 
  {
  # (BINT or num_str, BINT or num_str) return BINT
  # compute power of two numbers -- stolen from Knuth Vol 2 pg 233
  # modifies first argument
  my ($self,$x,$y,@r) = objectify(2,@_);

  return $x if $x->modify('bpow');

  return $upgrade->bpow($upgrade->new($x),$y,@r)
   if defined $upgrade && $y->isa($upgrade);

  $r[3] = $y;					# no push!
  return $x if $x->{sign} =~ /^[+-]inf$/;	# -inf/+inf ** x
  return $x->bnan() if $x->{sign} eq $nan || $y->{sign} eq $nan;
  return $x->bone(@r) if $y->is_zero();
  return $x->round(@r) if $x->is_one() || $y->is_one();
  if ($x->{sign} eq '-' && $CALC->_is_one($x->{value}))
    {
    # if $x == -1 and odd/even y => +1/-1
    return $y->is_odd() ? $x->round(@r) : $x->babs()->round(@r);
    # my Casio FX-5500L has a bug here: -1 ** 2 is -1, but -1 * -1 is 1;
    }
  # 1 ** -y => 1 / (1 ** |y|)
  # so do test for negative $y after above's clause
  return $x->bnan() if $y->{sign} eq '-';
  return $x->round(@r) if $x->is_zero();  # 0**y => 0 (if not y <= 0)

  if ($CALC->can('_pow'))
    {
    $x->{value} = $CALC->_pow($x->{value},$y->{value});
    return $x->round(@r);
    }

# based on the assumption that shifting in base 10 is fast, and that mul
# works faster if numbers are small: we count trailing zeros (this step is
# O(1)..O(N), but in case of O(N) we save much more time due to this),
# stripping them out of the multiplication, and add $count * $y zeros
# afterwards like this:
# 300 ** 3 == 300*300*300 == 3*3*3 . '0' x 2 * 3 == 27 . '0' x 6
# creates deep recursion?
#  my $zeros = $x->_trailing_zeros();
#  if ($zeros > 0)
#    {
#    $x->brsft($zeros,10);	# remove zeros
#    $x->bpow($y);		# recursion (will not branch into here again)
#    $zeros = $y * $zeros; 	# real number of zeros to add
#    $x->blsft($zeros,10);
#    return $x->round($a,$p,$r);
#    }

  my $pow2 = $self->__one();
  my $y1 = $class->new($y);
  my $two = $self->new(2);
  while (!$y1->is_one())
    {
    $pow2->bmul($x) if $y1->is_odd();
    $y1->bdiv($two);
    $x->bmul($x);
    }
  $x->bmul($pow2) unless $pow2->is_one();
  $x->round(@r);
  }

sub blsft 
  {
  # (BINT or num_str, BINT or num_str) return BINT
  # compute x << y, base n, y >= 0
  my ($self,$x,$y,$n,$a,$p,$r) = objectify(2,@_);
  
  return $x if $x->modify('blsft');
  return $x->bnan() if ($x->{sign} !~ /^[+-]$/ || $y->{sign} !~ /^[+-]$/);
  return $x->round($a,$p,$r) if $y->is_zero();

  $n = 2 if !defined $n; return $x->bnan() if $n <= 0 || $y->{sign} eq '-';

  my $t; $t = $CALC->_lsft($x->{value},$y->{value},$n) if $CALC->can('_lsft');
  if (defined $t)
    {
    $x->{value} = $t; return $x->round($a,$p,$r);
    }
  # fallback
  return $x->bmul( $self->bpow($n, $y, $a, $p, $r), $a, $p, $r );
  }

sub brsft 
  {
  # (BINT or num_str, BINT or num_str) return BINT
  # compute x >> y, base n, y >= 0
  my ($self,$x,$y,$n,$a,$p,$r) = objectify(2,@_);

  return $x if $x->modify('brsft');
  return $x->bnan() if ($x->{sign} !~ /^[+-]$/ || $y->{sign} !~ /^[+-]$/);
  return $x->round($a,$p,$r) if $y->is_zero();
  return $x->bzero($a,$p,$r) if $x->is_zero();		# 0 => 0

  $n = 2 if !defined $n; return $x->bnan() if $n <= 0 || $y->{sign} eq '-';

   # this only works for negative numbers when shifting in base 2
  if (($x->{sign} eq '-') && ($n == 2))
    {
    return $x->round($a,$p,$r) if $x->is_one('-');	# -1 => -1
    if (!$y->is_one())
      {
      # although this is O(N*N) in calc (as_bin!) it is O(N) in Pari et al
      # but perhaps there is a better emulation for two's complement shift...
      # if $y != 1, we must simulate it by doing:
      # convert to bin, flip all bits, shift, and be done
      $x->binc();			# -3 => -2
      my $bin = $x->as_bin();
      $bin =~ s/^-0b//;			# strip '-0b' prefix
      $bin =~ tr/10/01/;		# flip bits
      # now shift
      if (length($bin) <= $y)
        {
	$bin = '0'; 			# shifting to far right creates -1
					# 0, because later increment makes 
					# that 1, attached '-' makes it '-1'
					# because -1 >> x == -1 !
        } 
      else
	{
	$bin =~ s/.{$y}$//;		# cut off at the right side
        $bin = '1' . $bin;		# extend left side by one dummy '1'
        $bin =~ tr/10/01/;		# flip bits back
	}
      my $res = $self->new('0b'.$bin);	# add prefix and convert back
      $res->binc();			# remember to increment
      $x->{value} = $res->{value};	# take over value
      return $x->round($a,$p,$r);	# we are done now, magic, isn't?
      }
    $x->bdec();				# n == 2, but $y == 1: this fixes it
    }

  my $t; $t = $CALC->_rsft($x->{value},$y->{value},$n) if $CALC->can('_rsft');
  if (defined $t)
    {
    $x->{value} = $t;
    return $x->round($a,$p,$r);
    }
  # fallback
  $x->bdiv($self->bpow($n,$y, $a,$p,$r), $a,$p,$r);
  $x;
  }

sub band 
  {
  #(BINT or num_str, BINT or num_str) return BINT
  # compute x & y
  my ($self,$x,$y,$a,$p,$r) = objectify(2,@_);
  
  return $x if $x->modify('band');

  local $Math::BigInt::upgrade = undef;

  return $x->bnan() if ($x->{sign} !~ /^[+-]$/ || $y->{sign} !~ /^[+-]$/);
  return $x->bzero() if $y->is_zero() || $x->is_zero();

  my $sign = 0;					# sign of result
  $sign = 1 if ($x->{sign} eq '-') && ($y->{sign} eq '-');
  my $sx = 1; $sx = -1 if $x->{sign} eq '-';
  my $sy = 1; $sy = -1 if $y->{sign} eq '-';
  
  if ($CALC->can('_and') && $sx == 1 && $sy == 1)
    {
    $x->{value} = $CALC->_and($x->{value},$y->{value});
    return $x->round($a,$p,$r);
    }

  my $m = $self->bone(); my ($xr,$yr);
  my $x10000 = $self->new (0x1000);
  my $y1 = copy(ref($x),$y);	 		# make copy
  $y1->babs();					# and positive
  my $x1 = $x->copy()->babs(); $x->bzero();	# modify x in place!
  use integer;					# need this for negative bools
  while (!$x1->is_zero() && !$y1->is_zero())
    {
    ($x1, $xr) = bdiv($x1, $x10000);
    ($y1, $yr) = bdiv($y1, $x10000);
    # make both op's numbers!
    $x->badd( bmul( $class->new(
       abs($sx*int($xr->numify()) & $sy*int($yr->numify()))), 
      $m));
    $m->bmul($x10000);
    }
  $x->bneg() if $sign;
  return $x->round($a,$p,$r);
  }

sub bior 
  {
  #(BINT or num_str, BINT or num_str) return BINT
  # compute x | y
  my ($self,$x,$y,$a,$p,$r) = objectify(2,@_);

  return $x if $x->modify('bior');

  local $Math::BigInt::upgrade = undef;

  return $x->bnan() if ($x->{sign} !~ /^[+-]$/ || $y->{sign} !~ /^[+-]$/);
  return $x if $y->is_zero();

  my $sign = 0;					# sign of result
  $sign = 1 if ($x->{sign} eq '-') || ($y->{sign} eq '-');
  my $sx = 1; $sx = -1 if $x->{sign} eq '-';
  my $sy = 1; $sy = -1 if $y->{sign} eq '-';

  # don't use lib for negative values
  if ($CALC->can('_or') && $sx == 1 && $sy == 1)
    {
    $x->{value} = $CALC->_or($x->{value},$y->{value});
    return $x->round($a,$p,$r);
    }

  my $m = $self->bone(); my ($xr,$yr);
  my $x10000 = $self->new(0x10000);
  my $y1 = copy(ref($x),$y);	 		# make copy
  $y1->babs();					# and positive
  my $x1 = $x->copy()->babs(); $x->bzero();	# modify x in place!
  use integer;					# need this for negative bools
  while (!$x1->is_zero() || !$y1->is_zero())
    {
    ($x1, $xr) = bdiv($x1,$x10000);
    ($y1, $yr) = bdiv($y1,$x10000);
    # make both op's numbers!
    $x->badd( bmul( $class->new(
       abs($sx*int($xr->numify()) | $sy*int($yr->numify()))), 
      $m));
    $m->bmul($x10000);
    }
  $x->bneg() if $sign;
  return $x->round($a,$p,$r);
  }

sub bxor 
  {
  #(BINT or num_str, BINT or num_str) return BINT
  # compute x ^ y
  my ($self,$x,$y,$a,$p,$r) = objectify(2,@_);

  return $x if $x->modify('bxor');

  local $Math::BigInt::upgrade = undef;

  return $x->bnan() if ($x->{sign} !~ /^[+-]$/ || $y->{sign} !~ /^[+-]$/);
  return $x if $y->is_zero();
  
  my $sign = 0;					# sign of result
  $sign = 1 if $x->{sign} ne $y->{sign};
  my $sx = 1; $sx = -1 if $x->{sign} eq '-';
  my $sy = 1; $sy = -1 if $y->{sign} eq '-';

  # don't use lib for negative values
  if ($CALC->can('_xor') && $sx == 1 && $sy == 1)
    {
    $x->{value} = $CALC->_xor($x->{value},$y->{value});
    return $x->round($a,$p,$r);
    }

  my $m = $self->bone(); my ($xr,$yr);
  my $x10000 = $self->new(0x10000);
  my $y1 = copy(ref($x),$y);	 		# make copy
  $y1->babs();					# and positive
  my $x1 = $x->copy()->babs(); $x->bzero();	# modify x in place!
  use integer;					# need this for negative bools
  while (!$x1->is_zero() || !$y1->is_zero())
    {
    ($x1, $xr) = bdiv($x1, $x10000);
    ($y1, $yr) = bdiv($y1, $x10000);
    # make both op's numbers!
    $x->badd( bmul( $class->new(
       abs($sx*int($xr->numify()) ^ $sy*int($yr->numify()))), 
      $m));
    $m->bmul($x10000);
    }
  $x->bneg() if $sign;
  return $x->round($a,$p,$r);
  }

sub length
  {
  my ($self,$x) = ref($_[0]) ? (ref($_[0]),$_[0]) : objectify(1,@_);

  my $e = $CALC->_len($x->{value}); 
  return wantarray ? ($e,0) : $e;
  }

sub digit
  {
  # return the nth decimal digit, negative values count backward, 0 is right
  my ($self,$x,$n) = ref($_[0]) ? (ref($_[0]),@_) : objectify(1,@_);
  $n = 0 if !defined $n;

  $CALC->_digit($x->{value},$n);
  }

sub _trailing_zeros
  {
  # return the amount of trailing zeros in $x
  my $x = shift;
  $x = $class->new($x) unless ref $x;

  return 0 if $x->is_zero() || $x->is_odd() || $x->{sign} !~ /^[+-]$/;

  return $CALC->_zeros($x->{value}) if $CALC->can('_zeros');

  # if not: since we do not know underlying internal representation:
  my $es = "$x"; $es =~ /([0]*)$/;
  return 0 if !defined $1;	# no zeros
  return CORE::length("$1");	# as string, not as +0!
  }

sub bsqrt
  {
  my ($self,$x,$a,$p,$r) = ref($_[0]) ? (ref($_[0]),$_[0]) : objectify(1,@_);

  return $x if $x->modify('bsqrt');

  return $x->bnan() if $x->{sign} ne '+';	# -x or inf or NaN => NaN
  return $x->bzero($a,$p) if $x->is_zero();			# 0 => 0
  return $x->round($a,$p,$r) if $x->is_one();			# 1 => 1

  return $upgrade->bsqrt($x,$a,$p,$r) if defined $upgrade;

  if ($CALC->can('_sqrt'))
    {
    $x->{value} = $CALC->_sqrt($x->{value});
    return $x->round($a,$p,$r);
    }

  return $x->bone($a,$p) if $x < 4;				# 2,3 => 1
  my $y = $x->copy();
  my $l = int($x->length()/2);
  
  $x->bone();					# keep ref($x), but modify it
  $x->blsft($l,10);

  my $last = $self->bzero();
  my $two = $self->new(2);
  my $lastlast = $x+$two;
  while ($last != $x && $lastlast != $x)
    {
    $lastlast = $last; $last = $x; 
    $x += $y / $x; 
    $x /= $two;
    }
  $x-- if $x * $x > $y;				# overshot?
  $x->round($a,$p,$r);
  }

sub exponent
  {
  # return a copy of the exponent (here always 0, NaN or 1 for $m == 0)
  my ($self,$x) = ref($_[0]) ? (ref($_[0]),$_[0]) : objectify(1,@_);
 
  if ($x->{sign} !~ /^[+-]$/)
    {
    my $s = $x->{sign}; $s =~ s/^[+-]//;
    return $self->new($s); 		# -inf,+inf => inf
    }
  my $e = $class->bzero();
  return $e->binc() if $x->is_zero();
  $e += $x->_trailing_zeros();
  $e;
  }

sub mantissa
  {
  # return the mantissa (compatible to Math::BigFloat, e.g. reduced)
  my ($self,$x) = ref($_[0]) ? (ref($_[0]),$_[0]) : objectify(1,@_);

  if ($x->{sign} !~ /^[+-]$/)
    {
    return $self->new($x->{sign}); 		# keep + or - sign
    }
  my $m = $x->copy();
  # that's inefficient
  my $zeros = $m->_trailing_zeros();
  $m->brsft($zeros,10) if $zeros != 0;
#  $m /= 10 ** $zeros if $zeros != 0;
  $m;
  }

sub parts
  {
  # return a copy of both the exponent and the mantissa
  my ($self,$x) = ref($_[0]) ? (ref($_[0]),$_[0]) : objectify(1,@_);

  return ($x->mantissa(),$x->exponent());
  }
   
##############################################################################
# rounding functions

sub bfround
  {
  # precision: round to the $Nth digit left (+$n) or right (-$n) from the '.'
  # $n == 0 || $n == 1 => round to integer
  my $x = shift; $x = $class->new($x) unless ref $x;
  my ($scale,$mode) = $x->_scale_p($x->precision(),$x->round_mode(),@_);
  return $x if !defined $scale;		# no-op
  return $x if $x->modify('bfround');

  # no-op for BigInts if $n <= 0
  if ($scale <= 0)
    {
    $x->{_a} = undef;				# clear an eventual set A
    $x->{_p} = $scale; return $x;
    }

  $x->bround( $x->length()-$scale, $mode);
  $x->{_a} = undef;				# bround sets {_a}
  $x->{_p} = $scale;				# so correct it
  $x;
  }

sub _scan_for_nonzero
  {
  my $x = shift;
  my $pad = shift;
  my $xs = shift;
 
  my $len = $x->length();
  return 0 if $len == 1;		# '5' is trailed by invisible zeros
  my $follow = $pad - 1;
  return 0 if $follow > $len || $follow < 1;

  # since we do not know underlying represention of $x, use decimal string
  #my $r = substr ($$xs,-$follow);
  my $r = substr ("$x",-$follow);
  return 1 if $r =~ /[^0]/; return 0;
  }

sub fround
  {
  # to make life easier for switch between MBF and MBI (autoload fxxx()
  # like MBF does for bxxx()?)
  my $x = shift;
  return $x->bround(@_);
  }

sub bround
  {
  # accuracy: +$n preserve $n digits from left,
  #           -$n preserve $n digits from right (f.i. for 0.1234 style in MBF)
  # no-op for $n == 0
  # and overwrite the rest with 0's, return normalized number
  # do not return $x->bnorm(), but $x

  my $x = shift; $x = $class->new($x) unless ref $x;
  my ($scale,$mode) = $x->_scale_a($x->accuracy(),$x->round_mode(),@_);
  return $x if !defined $scale;			# no-op
  return $x if $x->modify('bround');
  
  if ($x->is_zero() || $scale == 0)
    {
    $x->{_a} = $scale if !defined $x->{_a} || $x->{_a} > $scale; # 3 > 2
    return $x;
    }
  return $x if $x->{sign} !~ /^[+-]$/;		# inf, NaN

  # we have fewer digits than we want to scale to
  my $len = $x->length();
  # scale < 0, but > -len (not >=!)
  if (($scale < 0 && $scale < -$len-1) || ($scale >= $len))
    {
    $x->{_a} = $scale if !defined $x->{_a} || $x->{_a} > $scale; # 3 > 2
    return $x; 
    }
   
  # count of 0's to pad, from left (+) or right (-): 9 - +6 => 3, or |-6| => 6
  my ($pad,$digit_round,$digit_after);
  $pad = $len - $scale;
  $pad = abs($scale-1) if $scale < 0;

  # do not use digit(), it is costly for binary => decimal

  my $xs = $CALC->_str($x->{value});
  my $pl = -$pad-1;
 
  # pad:   123: 0 => -1, at 1 => -2, at 2 => -3, at 3 => -4
  # pad+1: 123: 0 => 0,  at 1 => -1, at 2 => -2, at 3 => -3
  $digit_round = '0'; $digit_round = substr($$xs,$pl,1) if $pad <= $len;
  $pl++; $pl ++ if $pad >= $len;
  $digit_after = '0'; $digit_after = substr($$xs,$pl,1) if $pad > 0;

 #  print "$pad $pl $$xs dr $digit_round da $digit_after\n";

  # in case of 01234 we round down, for 6789 up, and only in case 5 we look
  # closer at the remaining digits of the original $x, remember decision
  my $round_up = 1;					# default round up
  $round_up -- if
    ($mode eq 'trunc')				||	# trunc by round down
    ($digit_after =~ /[01234]/)			|| 	# round down anyway,
							# 6789 => round up
    ($digit_after eq '5')			&&	# not 5000...0000
    ($x->_scan_for_nonzero($pad,$xs) == 0)		&&
    (
     ($mode eq 'even') && ($digit_round =~ /[24680]/) ||
     ($mode eq 'odd')  && ($digit_round =~ /[13579]/) ||
     ($mode eq '+inf') && ($x->{sign} eq '-')   ||
     ($mode eq '-inf') && ($x->{sign} eq '+')   ||
     ($mode eq 'zero')		# round down if zero, sign adjusted below
    );
  my $put_back = 0;					# not yet modified
	
  # old code, depend on internal representation
  # split mantissa at $pad and then pad with zeros
  #my $s5 = int($pad / 5);
  #my $i = 0;
  #while ($i < $s5)
  #  {
  #  $x->{value}->[$i++] = 0;				# replace with 5 x 0
  #  }
  #$x->{value}->[$s5] = '00000'.$x->{value}->[$s5];	# pad with 0
  #my $rem = $pad % 5;				# so much left over
  #if ($rem > 0)
  #  {
  #  #print "remainder $rem\n";
  ##  #print "elem      $x->{value}->[$s5]\n";
  #  substr($x->{value}->[$s5],-$rem,$rem) = '0' x $rem;	# stamp w/ '0'
  #  }
  #$x->{value}->[$s5] = int ($x->{value}->[$s5]);	# str '05' => int '5'
  #print ${$CALC->_str($pad->{value})}," $len\n";

  if (($pad > 0) && ($pad <= $len))
    {
    substr($$xs,-$pad,$pad) = '0' x $pad;
    $put_back = 1;
    }
  elsif ($pad > $len)
    {
    $x->bzero();					# round to '0'
    }

  if ($round_up)					# what gave test above?
    {
    $put_back = 1;
    $pad = $len, $$xs = '0'x$pad if $scale < 0;		# tlr: whack 0.51=>1.0	

    # we modify directly the string variant instead of creating a number and
    # adding it
    my $c = 0; $pad ++;				# for $pad == $len case
    while ($pad <= $len)
      {
      $c = substr($$xs,-$pad,1) + 1; $c = '0' if $c eq '10';
      substr($$xs,-$pad,1) = $c; $pad++;
      last if $c != 0;				# no overflow => early out
      }
    $$xs = '1'.$$xs if $c == 0;

    # $x->badd( Math::BigInt->new($x->{sign}.'1'. '0' x $pad) );
    }
  $x->{value} = $CALC->_new($xs) if $put_back == 1;	# put back in

  $x->{_a} = $scale if $scale >= 0;
  if ($scale < 0)
    {
    $x->{_a} = $len+$scale;
    $x->{_a} = 0 if $scale < -$len;
    }
  $x;
  }

sub bfloor
  {
  # return integer less or equal then number, since it is already integer,
  # always returns $self
  my ($self,$x,$a,$p,$r) = ref($_[0]) ? (ref($_[0]),@_) : objectify(1,@_);

  # not needed: return $x if $x->modify('bfloor');
  return $x->round($a,$p,$r);
  }

sub bceil
  {
  # return integer greater or equal then number, since it is already integer,
  # always returns $self
  my ($self,$x,$a,$p,$r) = ref($_[0]) ? (ref($_[0]),@_) : objectify(1,@_);

  # not needed: return $x if $x->modify('bceil');
  return $x->round($a,$p,$r);
  }

##############################################################################
# private stuff (internal use only)

sub __one
  {
  # internal speedup, set argument to 1, or create a +/- 1
  my $self = shift;
  my $x = $self->bone(); # $x->{value} = $CALC->_one();
  $x->{sign} = shift || '+';
  return $x;
  }

sub _swap
  {
  # Overload will swap params if first one is no object ref so that the first
  # one is always an object ref. In this case, third param is true.
  # This routine is to overcome the effect of scalar,$object creating an object
  # of the class of this package, instead of the second param $object. This
  # happens inside overload, when the overload section of this package is
  # inherited by sub classes.
  # For overload cases (and this is used only there), we need to preserve the
  # args, hence the copy().
  # You can override this method in a subclass, the overload section will call
  # $object->_swap() to make sure it arrives at the proper subclass, with some
  # exceptions like '+' and '-'. To make '+' and '-' work, you also need to
  # specify your own overload for them.

  # object, (object|scalar) => preserve first and make copy
  # scalar, object	    => swapped, re-swap and create new from first
  #                            (using class of second object, not $class!!)
  my $self = shift;			# for override in subclass
  if ($_[2])
    {
    my $c = ref ($_[0]) || $class; 	# fallback $class should not happen
    return ( $c->new($_[1]), $_[0] );
    }
  return ( $_[0]->copy(), $_[1] );
  }

sub objectify
  {
  # check for strings, if yes, return objects instead
 
  # the first argument is number of args objectify() should look at it will
  # return $count+1 elements, the first will be a classname. This is because
  # overloaded '""' calls bstr($object,undef,undef) and this would result in
  # useless objects beeing created and thrown away. So we cannot simple loop
  # over @_. If the given count is 0, all arguments will be used.
 
  # If the second arg is a ref, use it as class.
  # If not, try to use it as classname, unless undef, then use $class 
  # (aka Math::BigInt). The latter shouldn't happen,though.

  # caller:			   gives us:
  # $x->badd(1);                => ref x, scalar y
  # Class->badd(1,2);           => classname x (scalar), scalar x, scalar y
  # Class->badd( Class->(1),2); => classname x (scalar), ref x, scalar y
  # Math::BigInt::badd(1,2);    => scalar x, scalar y
  # In the last case we check number of arguments to turn it silently into
  # $class,1,2. (We can not take '1' as class ;o)
  # badd($class,1) is not supported (it should, eventually, try to add undef)
  # currently it tries 'Math::BigInt' + 1, which will not work.

  # some shortcut for the common cases

  # $x->unary_op();
  return (ref($_[1]),$_[1]) if (@_ == 2) && ($_[0]||0 == 1) && ref($_[1]);

  my $count = abs(shift || 0);
  
  my (@a,$k,$d);		# resulting array, temp, and downgrade 
  if (ref $_[0])
    {
    # okay, got object as first
    $a[0] = ref $_[0];
    }
  else
    {
    # nope, got 1,2 (Class->xxx(1) => Class,1 and not supported)
    $a[0] = $class;
    $a[0] = shift if $_[0] =~ /^[A-Z].*::/;	# classname as first?
    }
  no strict 'refs';
  # disable downgrading, because Math::BigFLoat->foo('1.0','2.0') needs floats
  if (defined ${"$a[0]::downgrade"})
    {
    $d = ${"$a[0]::downgrade"};
    ${"$a[0]::downgrade"} = undef;
    }

  # print "Now in objectify, my class is today $a[0]\n";
  if ($count == 0)
    {
    while (@_)
      {
      $k = shift;
      if (!ref($k))
        {
        $k = $a[0]->new($k);
        }
      elsif (ref($k) ne $a[0])
	{
	# foreign object, try to convert to integer
        $k->can('as_number') ?  $k = $k->as_number() : $k = $a[0]->new($k);
	}
      push @a,$k;
      }
    }
  else
    {
    while ($count > 0)
      {
      $count--; 
      $k = shift; 
      if (!ref($k))
        {
        $k = $a[0]->new($k);
        }
      elsif (ref($k) ne $a[0])
	{
	# foreign object, try to convert to integer
        $k->can('as_number') ?  $k = $k->as_number() : $k = $a[0]->new($k);
	}
      push @a,$k;
      }
    push @a,@_;		# return other params, too
    }
  die "$class objectify needs list context" unless wantarray;
  ${"$a[0]::downgrade"} = $d;
  @a;
  }

sub import 
  {
  my $self = shift;

  $IMPORT++;
  my @a = @_; my $l = scalar @_; my $j = 0;
  for ( my $i = 0; $i < $l ; $i++,$j++ )
    {
    if ($_[$i] eq ':constant')
      {
      # this causes overlord er load to step in
      overload::constant integer => sub { $self->new(shift) };
      overload::constant binary => sub { $self->new(shift) };
      splice @a, $j, 1; $j --;
      }
    elsif ($_[$i] eq 'upgrade')
      {
      # this causes upgrading
      $upgrade = $_[$i+1];		# or undef to disable
      my $s = 2; $s = 1 if @a-$j < 2;	# avoid "can not modify non-existant..."
      splice @a, $j, $s; $j -= $s;
      }
    elsif ($_[$i] =~ /^lib$/i)
      {
      # this causes a different low lib to take care...
      $CALC = $_[$i+1] || '';
      my $s = 2; $s = 1 if @a-$j < 2;	# avoid "can not modify non-existant..."
      splice @a, $j, $s; $j -= $s;
      }
    }
  # any non :constant stuff is handled by our parent, Exporter
  # even if @_ is empty, to give it a chance 
  $self->SUPER::import(@a);			# need it for subclasses
  $self->export_to_level(1,$self,@a);		# need it for MBF

  # try to load core math lib
  my @c = split /\s*,\s*/,$CALC;
  push @c,'Calc';				# if all fail, try this
  $CALC = '';					# signal error
  foreach my $lib (@c)
    {
    $lib = 'Math::BigInt::'.$lib if $lib !~ /^Math::BigInt/i;
    $lib =~ s/\.pm$//;
    if ($] < 5.006)
      {
      # Perl < 5.6.0 dies with "out of memory!" when eval() and ':constant' is
      # used in the same script, or eval inside import().
      (my $mod = $lib . '.pm') =~ s!::!/!g;
      # require does not automatically :: => /, so portability problems arise
      eval { require $mod; $lib->import( @c ); }
      }
    else
      {
      eval "use $lib qw/@c/;";
      }
    $CALC = $lib, last if $@ eq '';	# no error in loading lib?
    }
  die "Couldn't load any math lib, not even the default" if $CALC eq '';
  }

sub __from_hex
  {
  # convert a (ref to) big hex string to BigInt, return undef for error
  my $hs = shift;

  my $x = Math::BigInt->bzero();
  
  # strip underscores
  $$hs =~ s/([0-9a-fA-F])_([0-9a-fA-F])/$1$2/g;	
  $$hs =~ s/([0-9a-fA-F])_([0-9a-fA-F])/$1$2/g;	
  
  return $x->bnan() if $$hs !~ /^[\-\+]?0x[0-9A-Fa-f]+$/;

  my $sign = '+'; $sign = '-' if ($$hs =~ /^-/);

  $$hs =~ s/^[+-]//;			# strip sign
  if ($CALC->can('_from_hex'))
    {
    $x->{value} = $CALC->_from_hex($hs);
    }
  else
    {
    # fallback to pure perl
    my $mul = Math::BigInt->bzero(); $mul++;
    my $x65536 = Math::BigInt->new(65536);
    my $len = CORE::length($$hs)-2;
    $len = int($len/4);			# 4-digit parts, w/o '0x'
    my $val; my $i = -4;
    while ($len >= 0)
      {
      $val = substr($$hs,$i,4);
      $val =~ s/^[+-]?0x// if $len == 0;	# for last part only because
      $val = hex($val); 			# hex does not like wrong chars
      $i -= 4; $len --;
      $x += $mul * $val if $val != 0;
      $mul *= $x65536 if $len >= 0;		# skip last mul
      }
    }
  $x->{sign} = $sign unless $CALC->_is_zero($x->{value}); 	# no '-0'
  $x;
  }

sub __from_bin
  {
  # convert a (ref to) big binary string to BigInt, return undef for error
  my $bs = shift;

  my $x = Math::BigInt->bzero();
  # strip underscores
  $$bs =~ s/([01])_([01])/$1$2/g;	
  $$bs =~ s/([01])_([01])/$1$2/g;	
  return $x->bnan() if $$bs !~ /^[+-]?0b[01]+$/;

  my $sign = '+'; $sign = '-' if ($$bs =~ /^\-/);
  $$bs =~ s/^[+-]//;				# strip sign
  if ($CALC->can('_from_bin'))
    {
    $x->{value} = $CALC->_from_bin($bs);
    }
  else
    {
    my $mul = Math::BigInt->bzero(); $mul++;
    my $x256 = Math::BigInt->new(256);
    my $len = CORE::length($$bs)-2;
    $len = int($len/8);				# 8-digit parts, w/o '0b'
    my $val; my $i = -8;
    while ($len >= 0)
      {
      $val = substr($$bs,$i,8);
      $val =~ s/^[+-]?0b// if $len == 0;	# for last part only
      #$val = oct('0b'.$val);	# does not work on Perl prior to 5.6.0
      # slower:
      # $val = ('0' x (8-CORE::length($val))).$val if CORE::length($val) < 8;
      $val = ord(pack('B8',substr('00000000'.$val,-8,8)));
      $i -= 8; $len --;
      $x += $mul * $val if $val != 0;
      $mul *= $x256 if $len >= 0;		# skip last mul
      }
    }
  $x->{sign} = $sign unless $CALC->_is_zero($x->{value}); 	# no '-0'
  $x;
  }

sub _split
  {
  # (ref to num_str) return num_str
  # internal, take apart a string and return the pieces
  # strip leading/trailing whitespace, leading zeros, underscore and reject
  # invalid input
  my $x = shift;

  # strip white space at front, also extranous leading zeros
  $$x =~ s/^\s*([-]?)0*([0-9])/$1$2/g;	# will not strip '  .2'
  $$x =~ s/^\s+//;			# but this will			
  $$x =~ s/\s+$//g;			# strip white space at end

  # shortcut, if nothing to split, return early
  if ($$x =~ /^[+-]?\d+$/)
    {
    $$x =~ s/^([+-])0*([0-9])/$2/; my $sign = $1 || '+';
    return (\$sign, $x, \'', \'', \0);
    }

  # invalid starting char?
  return if $$x !~ /^[+-]?(\.?[0-9]|0b[0-1]|0x[0-9a-fA-F])/;

  return __from_hex($x) if $$x =~ /^[\-\+]?0x/;	# hex string
  return __from_bin($x) if $$x =~ /^[\-\+]?0b/;	# binary string
  
  # strip underscores between digits
  $$x =~ s/(\d)_(\d)/$1$2/g;
  $$x =~ s/(\d)_(\d)/$1$2/g;		# do twice for 1_2_3

  # some possible inputs: 
  # 2.1234 # 0.12        # 1 	      # 1E1 # 2.134E1 # 434E-10 # 1.02009E-2 
  # .2 	   # 1_2_3.4_5_6 # 1.4E1_2_3  # 1e3 # +.2

  return if $$x =~ /[Ee].*[Ee]/;	# more than one E => error

  my ($m,$e) = split /[Ee]/,$$x;
  $e = '0' if !defined $e || $e eq "";
  # sign,value for exponent,mantint,mantfrac
  my ($es,$ev,$mis,$miv,$mfv);
  # valid exponent?
  if ($e =~ /^([+-]?)0*(\d+)$/) # strip leading zeros
    {
    $es = $1; $ev = $2;
    # valid mantissa?
    return if $m eq '.' || $m eq '';
    my ($mi,$mf) = split /\./,$m;
    $mi = '0' if !defined $mi;
    $mi .= '0' if $mi =~ /^[\-\+]?$/;
    $mf = '0' if !defined $mf || $mf eq '';
    if ($mi =~ /^([+-]?)0*(\d+)$/) # strip leading zeros
      {
      $mis = $1||'+'; $miv = $2;
      return unless ($mf =~ /^(\d*?)0*$/);	# strip trailing zeros
      $mfv = $1;
      return (\$mis,\$miv,\$mfv,\$es,\$ev);
      }
    }
  return; # NaN, not a number
  }

sub as_number
  {
  # an object might be asked to return itself as bigint on certain overloaded
  # operations, this does exactly this, so that sub classes can simple inherit
  # it or override with their own integer conversion routine
  my $self = shift;

  $self->copy();
  }

sub as_hex
  {
  # return as hex string, with prefixed 0x
  my $x = shift; $x = $class->new($x) if !ref($x);

  return $x->bstr() if $x->{sign} !~ /^[+-]$/;	# inf, nan etc
  return '0x0' if $x->is_zero();

  my $es = ''; my $s = '';
  $s = $x->{sign} if $x->{sign} eq '-';
  if ($CALC->can('_as_hex'))
    {
    $es = ${$CALC->_as_hex($x->{value})};
    }
  else
    {
    my $x1 = $x->copy()->babs(); my $xr;
    my $x10000 = Math::BigInt->new (0x10000);
    while (!$x1->is_zero())
      {
      ($x1, $xr) = bdiv($x1,$x10000);
      $es .= unpack('h4',pack('v',$xr->numify()));
      }
    $es = reverse $es;
    $es =~ s/^[0]+//; 	# strip leading zeros
    $s .= '0x';
    }
  $s . $es;
  }

sub as_bin
  {
  # return as binary string, with prefixed 0b
  my $x = shift; $x = $class->new($x) if !ref($x);

  return $x->bstr() if $x->{sign} !~ /^[+-]$/;	# inf, nan etc
  return '0b0' if $x->is_zero();

  my $es = ''; my $s = '';
  $s = $x->{sign} if $x->{sign} eq '-';
  if ($CALC->can('_as_bin'))
    {
    $es = ${$CALC->_as_bin($x->{value})};
    }
  else
    {
    my $x1 = $x->copy()->babs(); my $xr;
    my $x10000 = Math::BigInt->new (0x10000);
    while (!$x1->is_zero())
      {
      ($x1, $xr) = bdiv($x1,$x10000);
      $es .= unpack('b16',pack('v',$xr->numify()));
      }
    $es = reverse $es; 
    $es =~ s/^[0]+//; 	# strip leading zeros
    $s .= '0b';
    }
  $s . $es;
  }

##############################################################################
# internal calculation routines (others are in Math::BigInt::Calc etc)

sub __lcm 
  { 
  # (BINT or num_str, BINT or num_str) return BINT
  # does modify first argument
  # LCM
 
  my $x = shift; my $ty = shift;
  return $x->bnan() if ($x->{sign} eq $nan) || ($ty->{sign} eq $nan);
  return $x * $ty / bgcd($x,$ty);
  }

sub __gcd
  { 
  # (BINT or num_str, BINT or num_str) return BINT
  # does modify both arguments
  # GCD -- Euclids algorithm E, Knuth Vol 2 pg 296
  my ($x,$ty) = @_;

  return $x->bnan() if $x->{sign} !~ /^[+-]$/ || $ty->{sign} !~ /^[+-]$/;

  while (!$ty->is_zero())
    {
    ($x, $ty) = ($ty,bmod($x,$ty));
    }
  $x;
  }

###############################################################################
# this method return 0 if the object can be modified, or 1 for not
# We use a fast use constant statement here, to avoid costly calls. Subclasses
# may override it with special code (f.i. Math::BigInt::Constant does so)

sub modify () { 0; }

1;
__END__

=head1 NAME

Math::BigInt - Arbitrary size integer math package

=head1 SYNOPSIS

  use Math::BigInt;

  # Number creation	
  $x = Math::BigInt->new($str);		# defaults to 0
  $nan  = Math::BigInt->bnan(); 	# create a NotANumber
  $zero = Math::BigInt->bzero();	# create a +0
  $inf = Math::BigInt->binf();		# create a +inf
  $inf = Math::BigInt->binf('-');	# create a -inf
  $one = Math::BigInt->bone();		# create a +1
  $one = Math::BigInt->bone('-');	# create a -1

  # Testing
  $x->is_zero();		# true if arg is +0
  $x->is_nan();			# true if arg is NaN
  $x->is_one();			# true if arg is +1
  $x->is_one('-');		# true if arg is -1
  $x->is_odd();			# true if odd, false for even
  $x->is_even();		# true if even, false for odd
  $x->is_positive();		# true if >= 0
  $x->is_negative();		# true if <  0
  $x->is_inf(sign);		# true if +inf, or -inf (sign is default '+')
  $x->is_int();			# true if $x is an integer (not a float)

  $x->bcmp($y);			# compare numbers (undef,<0,=0,>0)
  $x->bacmp($y);		# compare absolutely (undef,<0,=0,>0)
  $x->sign();			# return the sign, either +,- or NaN
  $x->digit($n);		# return the nth digit, counting from right
  $x->digit(-$n);		# return the nth digit, counting from left

  # The following all modify their first argument:

  # set 
  $x->bzero();			# set $x to 0
  $x->bnan();			# set $x to NaN
  $x->bone();			# set $x to +1
  $x->bone('-');		# set $x to -1
  $x->binf();			# set $x to inf
  $x->binf('-');		# set $x to -inf

  $x->bneg();			# negation
  $x->babs();			# absolute value
  $x->bnorm();			# normalize (no-op)
  $x->bnot();			# two's complement (bit wise not)
  $x->binc();			# increment x by 1
  $x->bdec();			# decrement x by 1
  
  $x->badd($y);			# addition (add $y to $x)
  $x->bsub($y);			# subtraction (subtract $y from $x)
  $x->bmul($y);			# multiplication (multiply $x by $y)
  $x->bdiv($y);			# divide, set $x to quotient
				# return (quo,rem) or quo if scalar

  $x->bmod($y);			# modulus (x % y)
  $x->bpow($y);			# power of arguments (x ** y)
  $x->blsft($y);		# left shift
  $x->brsft($y);		# right shift 
  $x->blsft($y,$n);		# left shift, by base $n (like 10)
  $x->brsft($y,$n);		# right shift, by base $n (like 10)
  
  $x->band($y);			# bitwise and
  $x->bior($y);			# bitwise inclusive or
  $x->bxor($y);			# bitwise exclusive or
  $x->bnot();			# bitwise not (two's complement)

  $x->bsqrt();			# calculate square-root
  $x->bfac();			# factorial of $x (1*2*3*4*..$x)

  $x->round($A,$P,$round_mode); # round to accuracy or precision using mode $r
  $x->bround($N);               # accuracy: preserve $N digits
  $x->bfround($N);              # round to $Nth digit, no-op for BigInts

  # The following do not modify their arguments in BigInt, but do in BigFloat:
  $x->bfloor();			# return integer less or equal than $x
  $x->bceil();			# return integer greater or equal than $x
  
  # The following do not modify their arguments:

  bgcd(@values);		# greatest common divisor (no OO style)
  blcm(@values);		# lowest common multiplicator (no OO style)
 
  $x->length();			# return number of digits in number
  ($x,$f) = $x->length();	# length of number and length of fraction part,
				# latter is always 0 digits long for BigInt's

  $x->exponent();		# return exponent as BigInt
  $x->mantissa();		# return (signed) mantissa as BigInt
  $x->parts();			# return (mantissa,exponent) as BigInt
  $x->copy();			# make a true copy of $x (unlike $y = $x;)
  $x->as_number();		# return as BigInt (in BigInt: same as copy())
  
  # conversation to string 
  $x->bstr();			# normalized string
  $x->bsstr();			# normalized string in scientific notation
  $x->as_hex();			# as signed hexadecimal string with prefixed 0x
  $x->as_bin();			# as signed binary string with prefixed 0b

=head1 DESCRIPTION

All operators (inlcuding basic math operations) are overloaded if you
declare your big integers as

  $i = new Math::BigInt '123_456_789_123_456_789';

Operations with overloaded operators preserve the arguments which is
exactly what you expect.

=over 2

=item Canonical notation

Big integer values are strings of the form C</^[+-]\d+$/> with leading
zeros suppressed.

   '-0'                            canonical value '-0', normalized '0'
   '   -123_123_123'               canonical value '-123123123'
   '1_23_456_7890'                 canonical value '1234567890'

=item Input

Input values to these routines may be either Math::BigInt objects or
strings of the form C</^\s*[+-]?[\d]+\.?[\d]*E?[+-]?[\d]*$/>.

You can include one underscore between any two digits.

This means integer values like 1.01E2 or even 1000E-2 are also accepted.
Non integer values result in NaN.

Math::BigInt::new() defaults to 0, while Math::BigInt::new('') results
in 'NaN'.

bnorm() on a BigInt object is now effectively a no-op, since the numbers 
are always stored in normalized form. On a string, it creates a BigInt 
object.

=item Output

Output values are BigInt objects (normalized), except for bstr(), which
returns a string in normalized form.
Some routines (C<is_odd()>, C<is_even()>, C<is_zero()>, C<is_one()>,
C<is_nan()>) return true or false, while others (C<bcmp()>, C<bacmp()>)
return either undef, <0, 0 or >0 and are suited for sort.

=back

=head1 METHODS

Each of the methods below accepts three additional parameters. These arguments
$A, $P and $R are accuracy, precision and round_mode. Please see more in the
section about ACCURACY and ROUNDIND.

=head2 accuracy

	$x->accuracy(5);		# local for $x
	$class->accuracy(5);		# global for all members of $class

Set or get the global or local accuracy, aka how many significant digits the
results have. Please see the section about L<ACCURACY AND PRECISION> for
further details.

Value must be greater than zero. Pass an undef value to disable it:

	$x->accuracy(undef);
	Math::BigInt->accuracy(undef);

Returns the current accuracy. For C<$x->accuracy()> it will return either the
local accuracy, or if not defined, the global. This means the return value
represents the accuracy that will be in effect for $x:

	$y = Math::BigInt->new(1234567);	# unrounded
	print Math::BigInt->accuracy(4),"\n";	# set 4, print 4
	$x = Math::BigInt->new(123456);		# will be automatically rounded
	print "$x $y\n";			# '123500 1234567'
	print $x->accuracy(),"\n";		# will be 4
	print $y->accuracy(),"\n";		# also 4, since global is 4
	print Math::BigInt->accuracy(5),"\n";	# set to 5, print 5
	print $x->accuracy(),"\n";		# still 4
	print $y->accuracy(),"\n";		# 5, since global is 5

=head2 brsft

	$x->brsft($y,$n);		

Shifts $x right by $y in base $n. Default is base 2, used are usually 10 and
2, but others work, too.

Right shifting usually amounts to dividing $x by $n ** $y and truncating the
result:


	$x = Math::BigInt->new(10);
	$x->brsft(1);			# same as $x >> 1: 5
	$x = Math::BigInt->new(1234);
	$x->brsft(2,10);		# result 12

There is one exception, and that is base 2 with negative $x:


	$x = Math::BigInt->new(-5);
	print $x->brsft(1);

This will print -3, not -2 (as it would if you divide -5 by 2 and truncate the
result).

=head2 new

  	$x = Math::BigInt->new($str,$A,$P,$R);

Creates a new BigInt object from a string or another BigInt object. The
input is accepted as decimal, hex (with leading '0x') or binary (with leading
'0b').

=head2 bnan

  	$x = Math::BigInt->bnan();

Creates a new BigInt object representing NaN (Not A Number).
If used on an object, it will set it to NaN:

	$x->bnan();

=head2 bzero

  	$x = Math::BigInt->bzero();

Creates a new BigInt object representing zero.
If used on an object, it will set it to zero:

	$x->bzero();

=head2 binf

  	$x = Math::BigInt->binf($sign);

Creates a new BigInt object representing infinity. The optional argument is
either '-' or '+', indicating whether you want infinity or minus infinity.
If used on an object, it will set it to infinity:

	$x->binf();
	$x->binf('-');

=head2 bone

  	$x = Math::BigInt->binf($sign);

Creates a new BigInt object representing one. The optional argument is
either '-' or '+', indicating whether you want one or minus one.
If used on an object, it will set it to one:

	$x->bone();		# +1
	$x->bone('-');		# -1

=head2 is_one()/is_zero()/is_nan()/is_inf()

  
	$x->is_zero();			# true if arg is +0
	$x->is_nan();			# true if arg is NaN
	$x->is_one();			# true if arg is +1
	$x->is_one('-');		# true if arg is -1
	$x->is_inf();			# true if +inf
	$x->is_inf('-');		# true if -inf (sign is default '+')

These methods all test the BigInt for beeing one specific value and return
true or false depending on the input. These are faster than doing something
like:

	if ($x == 0)

=head2 is_positive()/is_negative()
	
	$x->is_positive();		# true if >= 0
	$x->is_negative();		# true if <  0

The methods return true if the argument is positive or negative, respectively.
C<NaN> is neither positive nor negative, while C<+inf> counts as positive, and
C<-inf> is negative. A C<zero> is positive.

These methods are only testing the sign, and not the value.

=head2 is_odd()/is_even()/is_int()

	$x->is_odd();			# true if odd, false for even
	$x->is_even();			# true if even, false for odd
	$x->is_int();			# true if $x is an integer

The return true when the argument satisfies the condition. C<NaN>, C<+inf>,
C<-inf> are not integers and are neither odd nor even.

=head2 bcmp

	$x->bcmp($y);

Compares $x with $y and takes the sign into account.
Returns -1, 0, 1 or undef.

=head2 bacmp

	$x->bacmp($y);

Compares $x with $y while ignoring their. Returns -1, 0, 1 or undef.

=head2 sign

	$x->sign();

Return the sign, of $x, meaning either C<+>, C<->, C<-inf>, C<+inf> or NaN.

=head2 bcmp

  $x->digit($n);		# return the nth digit, counting from right

=head2 bneg

	$x->bneg();

Negate the number, e.g. change the sign between '+' and '-', or between '+inf'
and '-inf', respectively. Does nothing for NaN or zero.

=head2 babs

	$x->babs();

Set the number to it's absolute value, e.g. change the sign from '-' to '+'
and from '-inf' to '+inf', respectively. Does nothing for NaN or positive
numbers.

=head2 bnorm

  $x->bnorm();			# normalize (no-op)

=head2 bnot

  $x->bnot();			# two's complement (bit wise not)

=head2 binc

  $x->binc();			# increment x by 1

=head2 bdec

  $x->bdec();			# decrement x by 1

=head2 badd

  $x->badd($y);			# addition (add $y to $x)

=head2 bsub

  $x->bsub($y);			# subtraction (subtract $y from $x)

=head2 bmul

  $x->bmul($y);			# multiplication (multiply $x by $y)

=head2 bdiv

  $x->bdiv($y);			# divide, set $x to quotient
				# return (quo,rem) or quo if scalar

=head2 bmod

  $x->bmod($y);			# modulus (x % y)

=head2 bpow

  $x->bpow($y);			# power of arguments (x ** y)

=head2 blsft

  $x->blsft($y);		# left shift
  $x->blsft($y,$n);		# left shift, by base $n (like 10)

=head2 brsft

  $x->brsft($y);		# right shift 
  $x->brsft($y,$n);		# right shift, by base $n (like 10)

=head2 band

  $x->band($y);			# bitwise and

=head2 bior

  $x->bior($y);			# bitwise inclusive or

=head2 bxor

  $x->bxor($y);			# bitwise exclusive or

=head2 bnot

  $x->bnot();			# bitwise not (two's complement)

=head2 bsqrt

  $x->bsqrt();			# calculate square-root

=head2 bfac

  $x->bfac();			# factorial of $x (1*2*3*4*..$x)

=head2 round

  $x->round($A,$P,$round_mode); # round to accuracy or precision using mode $r

=head2 bround

  $x->bround($N);               # accuracy: preserve $N digits

=head2 bfround

  $x->bfround($N);              # round to $Nth digit, no-op for BigInts

=head2 bfloor

	$x->bfloor();			

Set $x to the integer less or equal than $x. This is a no-op in BigInt, but
does change $x in BigFloat.

=head2 bceil

	$x->bceil();

Set $x to the integer greater or equal than $x. This is a no-op in BigInt, but
does change $x in BigFloat.

=head2 bgcd

  bgcd(@values);		# greatest common divisor (no OO style)

=head2 blcm

  blcm(@values);		# lowest common multiplicator (no OO style)
 
head2 length

	$x->length();
        ($xl,$fl) = $x->length();

Returns the number of digits in the decimal representation of the number.
In list context, returns the length of the integer and fraction part. For
BigInt's, the length of the fraction part will always be 0.

=head2 exponent

	$x->exponent();

Return the exponent of $x as BigInt.

=head2 mantissa

	$x->mantissa();

Return the signed mantissa of $x as BigInt.

=head2 parts

  $x->parts();			# return (mantissa,exponent) as BigInt

=head2 copy

  $x->copy();			# make a true copy of $x (unlike $y = $x;)

=head2 as_number

  $x->as_number();		# return as BigInt (in BigInt: same as copy())
  
=head2 bsrt

  $x->bstr();			# normalized string

=head2 bsstr

  $x->bsstr();			# normalized string in scientific notation

=head2 as_hex

  $x->as_hex();			# as signed hexadecimal string with prefixed 0x

=head2 as_bin

  $x->as_bin();			# as signed binary string with prefixed 0b

=head1 ACCURACY and PRECISION

Since version v1.33, Math::BigInt and Math::BigFloat have full support for
accuracy and precision based rounding, both automatically after every
operation as well as manually.

This section describes the accuracy/precision handling in Math::Big* as it
used to be and as it is now, complete with an explanation of all terms and
abbreviations.

Not yet implemented things (but with correct description) are marked with '!',
things that need to be answered are marked with '?'.

In the next paragraph follows a short description of terms used here (because
these may differ from terms used by others people or documentation).

During the rest of this document, the shortcuts A (for accuracy), P (for
precision), F (fallback) and R (rounding mode) will be used.

=head2 Precision P

A fixed number of digits before (positive) or after (negative)
the decimal point. For example, 123.45 has a precision of -2. 0 means an
integer like 123 (or 120). A precision of 2 means two digits to the left
of the decimal point are zero, so 123 with P = 1 becomes 120. Note that
numbers with zeros before the decimal point may have different precisions,
because 1200 can have p = 0, 1 or 2 (depending on what the inital value
was). It could also have p < 0, when the digits after the decimal point
are zero.

The string output (of floating point numbers) will be padded with zeros:
 
	Initial value   P       A	Result          String
	------------------------------------------------------------
	1234.01         -3      	1000            1000
	1234            -2      	1200            1200
	1234.5          -1      	1230            1230
	1234.001        1       	1234            1234.0
	1234.01         0       	1234            1234
	1234.01         2       	1234.01		1234.01
	1234.01         5       	1234.01		1234.01000

For BigInts, no padding occurs.

=head2 Accuracy A

Number of significant digits. Leading zeros are not counted. A
number may have an accuracy greater than the non-zero digits
when there are zeros in it or trailing zeros. For example, 123.456 has
A of 6, 10203 has 5, 123.0506 has 7, 123.450000 has 8 and 0.000123 has 3.

The string output (of floating point numbers) will be padded with zeros:

	Initial value   P       A	Result          String
	------------------------------------------------------------
	1234.01			3	1230		1230
	1234.01			6	1234.01		1234.01
	1234.1			8	1234.1		1234.1000

For BigInts, no padding occurs.

=head2 Fallback F

When both A and P are undefined, this is used as a fallback accuracy when
dividing numbers.

=head2 Rounding mode R

When rounding a number, different 'styles' or 'kinds'
of rounding are possible. (Note that random rounding, as in
Math::Round, is not implemented.)

=over 2

=item 'trunc'

truncation invariably removes all digits following the
rounding place, replacing them with zeros. Thus, 987.65 rounded
to tens (P=1) becomes 980, and rounded to the fourth sigdig
becomes 987.6 (A=4). 123.456 rounded to the second place after the
decimal point (P=-2) becomes 123.46.

All other implemented styles of rounding attempt to round to the
"nearest digit." If the digit D immediately to the right of the
rounding place (skipping the decimal point) is greater than 5, the
number is incremented at the rounding place (possibly causing a
cascade of incrementation): e.g. when rounding to units, 0.9 rounds
to 1, and -19.9 rounds to -20. If D < 5, the number is similarly
truncated at the rounding place: e.g. when rounding to units, 0.4
rounds to 0, and -19.4 rounds to -19.

However the results of other styles of rounding differ if the
digit immediately to the right of the rounding place (skipping the
decimal point) is 5 and if there are no digits, or no digits other
than 0, after that 5. In such cases:

=item 'even'

rounds the digit at the rounding place to 0, 2, 4, 6, or 8
if it is not already. E.g., when rounding to the first sigdig, 0.45
becomes 0.4, -0.55 becomes -0.6, but 0.4501 becomes 0.5.

=item 'odd'

rounds the digit at the rounding place to 1, 3, 5, 7, or 9 if
it is not already. E.g., when rounding to the first sigdig, 0.45
becomes 0.5, -0.55 becomes -0.5, but 0.5501 becomes 0.6.

=item '+inf'

round to plus infinity, i.e. always round up. E.g., when
rounding to the first sigdig, 0.45 becomes 0.5, -0.55 becomes -0.5,
and 0.4501 also becomes 0.5.

=item '-inf'

round to minus infinity, i.e. always round down. E.g., when
rounding to the first sigdig, 0.45 becomes 0.4, -0.55 becomes -0.6,
but 0.4501 becomes 0.5.

=item 'zero'

round to zero, i.e. positive numbers down, negative ones up.
E.g., when rounding to the first sigdig, 0.45 becomes 0.4, -0.55
becomes -0.5, but 0.4501 becomes 0.5.

=back

The handling of A & P in MBI/MBF (the old core code shipped with Perl
versions <= 5.7.2) is like this:

=over 2

=item Precision

  * ffround($p) is able to round to $p number of digits after the decimal
    point
  * otherwise P is unused

=item Accuracy (significant digits)

  * fround($a) rounds to $a significant digits
  * only fdiv() and fsqrt() take A as (optional) paramater
    + other operations simply create the same number (fneg etc), or more (fmul)
      of digits
    + rounding/truncating is only done when explicitly calling one of fround
      or ffround, and never for BigInt (not implemented)
  * fsqrt() simply hands its accuracy argument over to fdiv.
  * the documentation and the comment in the code indicate two different ways
    on how fdiv() determines the maximum number of digits it should calculate,
    and the actual code does yet another thing
    POD:
      max($Math::BigFloat::div_scale,length(dividend)+length(divisor))
    Comment:
      result has at most max(scale, length(dividend), length(divisor)) digits
    Actual code:
      scale = max(scale, length(dividend)-1,length(divisor)-1);
      scale += length(divisior) - length(dividend);
    So for lx = 3, ly = 9, scale = 10, scale will actually be 16 (10+9-3).
    Actually, the 'difference' added to the scale is calculated from the
    number of "significant digits" in dividend and divisor, which is derived
    by looking at the length of the mantissa. Which is wrong, since it includes
    the + sign (oups) and actually gets 2 for '+100' and 4 for '+101'. Oups
    again. Thus 124/3 with div_scale=1 will get you '41.3' based on the strange
    assumption that 124 has 3 significant digits, while 120/7 will get you
    '17', not '17.1' since 120 is thought to have 2 significant digits.
    The rounding after the division then uses the remainder and $y to determine
    wether it must round up or down.
 ?  I have no idea which is the right way. That's why I used a slightly more
 ?  simple scheme and tweaked the few failing testcases to match it.

=back

This is how it works now:

=over 2

=item Setting/Accessing

  * You can set the A global via Math::BigInt->accuracy() or
    Math::BigFloat->accuracy() or whatever class you are using.
  * You can also set P globally by using Math::SomeClass->precision() likewise.
  * Globals are classwide, and not inherited by subclasses.
  * to undefine A, use Math::SomeCLass->accuracy(undef);
  * to undefine P, use Math::SomeClass->precision(undef);
  * Setting Math::SomeClass->accuracy() clears automatically
    Math::SomeClass->precision(), and vice versa.
  * To be valid, A must be > 0, P can have any value.
  * If P is negative, this means round to the P'th place to the right of the
    decimal point; positive values mean to the left of the decimal point.
    P of 0 means round to integer.
  * to find out the current global A, take Math::SomeClass->accuracy()
  * to find out the current global P, take Math::SomeClass->precision()
  * use $x->accuracy() respective $x->precision() for the local setting of $x.
  * Please note that $x->accuracy() respecive $x->precision() fall back to the
    defined globals, when $x's A or P is not set.

=item Creating numbers

  * When you create a number, you can give it's desired A or P via:
    $x = Math::BigInt->new($number,$A,$P);
  * Only one of A or P can be defined, otherwise the result is NaN
  * If no A or P is give ($x = Math::BigInt->new($number) form), then the
    globals (if set) will be used. Thus changing the global defaults later on
    will not change the A or P of previously created numbers (i.e., A and P of
    $x will be what was in effect when $x was created)
  * If given undef for A and P, B<no> rounding will occur, and the globals will
    B<not> be used. This is used by subclasses to create numbers without
    suffering rounding in the parent. Thus a subclass is able to have it's own
    globals enforced upon creation of a number by using
    $x = Math::BigInt->new($number,undef,undef):

	use Math::Bigint::SomeSubclass;
	use Math::BigInt;

	Math::BigInt->accuracy(2);
	Math::BigInt::SomeSubClass->accuracy(3);
	$x = Math::BigInt::SomeSubClass->new(1234);	

    $x is now 1230, and not 1200. A subclass might choose to implement
    this otherwise, e.g. falling back to the parent's A and P.

=item Usage

  * If A or P are enabled/defined, they are used to round the result of each
    operation according to the rules below
  * Negative P is ignored in Math::BigInt, since BigInts never have digits
    after the decimal point
  * Math::BigFloat uses Math::BigInts internally, but setting A or P inside
    Math::BigInt as globals should not tamper with the parts of a BigFloat.
    Thus a flag is used to mark all Math::BigFloat numbers as 'never round'

=item Precedence

  * It only makes sense that a number has only one of A or P at a time.
    Since you can set/get both A and P, there is a rule that will practically
    enforce only A or P to be in effect at a time, even if both are set.
    This is called precedence.
  * If two objects are involved in an operation, and one of them has A in
    effect, and the other P, this results in an error (NaN).
  * A takes precendence over P (Hint: A comes before P). If A is defined, it
    is used, otherwise P is used. If neither of them is defined, nothing is
    used, i.e. the result will have as many digits as it can (with an
    exception for fdiv/fsqrt) and will not be rounded.
  * There is another setting for fdiv() (and thus for fsqrt()). If neither of
    A or P is defined, fdiv() will use a fallback (F) of $div_scale digits.
    If either the dividend's or the divisor's mantissa has more digits than
    the value of F, the higher value will be used instead of F.
    This is to limit the digits (A) of the result (just consider what would
    happen with unlimited A and P in the case of 1/3 :-)
  * fdiv will calculate (at least) 4 more digits than required (determined by
    A, P or F), and, if F is not used, round the result
    (this will still fail in the case of a result like 0.12345000000001 with A
    or P of 5, but this can not be helped - or can it?)
  * Thus you can have the math done by on Math::Big* class in three modes:
    + never round (this is the default):
      This is done by setting A and P to undef. No math operation
      will round the result, with fdiv() and fsqrt() as exceptions to guard
      against overflows. You must explicitely call bround(), bfround() or
      round() (the latter with parameters).
      Note: Once you have rounded a number, the settings will 'stick' on it
      and 'infect' all other numbers engaged in math operations with it, since
      local settings have the highest precedence. So, to get SaferRound[tm],
      use a copy() before rounding like this:

        $x = Math::BigFloat->new(12.34);
        $y = Math::BigFloat->new(98.76);
        $z = $x * $y;                           # 1218.6984
        print $x->copy()->fround(3);            # 12.3 (but A is now 3!)
        $z = $x * $y;                           # still 1218.6984, without
                                                # copy would have been 1210!

    + round after each op:
      After each single operation (except for testing like is_zero()), the
      method round() is called and the result is rounded appropriately. By
      setting proper values for A and P, you can have all-the-same-A or
      all-the-same-P modes. For example, Math::Currency might set A to undef,
      and P to -2, globally.

 ?Maybe an extra option that forbids local A & P settings would be in order,
 ?so that intermediate rounding does not 'poison' further math? 

=item Overriding globals

  * you will be able to give A, P and R as an argument to all the calculation
    routines; the second parameter is A, the third one is P, and the fourth is
    R (shift right by one for binary operations like badd). P is used only if
    the first parameter (A) is undefined. These three parameters override the
    globals in the order detailed as follows, i.e. the first defined value
    wins:
    (local: per object, global: global default, parameter: argument to sub)
      + parameter A
      + parameter P
      + local A (if defined on both of the operands: smaller one is taken)
      + local P (if defined on both of the operands: bigger one is taken)
      + global A
      + global P
      + global F
  * fsqrt() will hand its arguments to fdiv(), as it used to, only now for two
    arguments (A and P) instead of one

=item Local settings

  * You can set A and P locally by using $x->accuracy() and $x->precision()
    and thus force different A and P for different objects/numbers.
  * Setting A or P this way immediately rounds $x to the new value.
  * $x->accuracy() clears $x->precision(), and vice versa.

=item Rounding

  * the rounding routines will use the respective global or local settings.
    fround()/bround() is for accuracy rounding, while ffround()/bfround()
    is for precision
  * the two rounding functions take as the second parameter one of the
    following rounding modes (R):
    'even', 'odd', '+inf', '-inf', 'zero', 'trunc'
  * you can set and get the global R by using Math::SomeClass->round_mode()
    or by setting $Math::SomeClass::round_mode
  * after each operation, $result->round() is called, and the result may
    eventually be rounded (that is, if A or P were set either locally,
    globally or as parameter to the operation)
  * to manually round a number, call $x->round($A,$P,$round_mode);
    this will round the number by using the appropriate rounding function
    and then normalize it.
  * rounding modifies the local settings of the number:

        $x = Math::BigFloat->new(123.456);
        $x->accuracy(5);
        $x->bround(4);

    Here 4 takes precedence over 5, so 123.5 is the result and $x->accuracy()
    will be 4 from now on.

=item Default values

  * R: 'even'
  * F: 40
  * A: undef
  * P: undef

=item Remarks

  * The defaults are set up so that the new code gives the same results as
    the old code (except in a few cases on fdiv):
    + Both A and P are undefined and thus will not be used for rounding
      after each operation.
    + round() is thus a no-op, unless given extra parameters A and P

=back

=head1 INTERNALS

The actual numbers are stored as unsigned big integers (with seperate sign).
You should neither care about nor depend on the internal representation; it
might change without notice. Use only method calls like C<< $x->sign(); >>
instead relying on the internal hash keys like in C<< $x->{sign}; >>. 

=head2 MATH LIBRARY

Math with the numbers is done (by default) by a module called
Math::BigInt::Calc. This is equivalent to saying:

	use Math::BigInt lib => 'Calc';

You can change this by using:

	use Math::BigInt lib => 'BitVect';

The following would first try to find Math::BigInt::Foo, then
Math::BigInt::Bar, and when this also fails, revert to Math::BigInt::Calc:

	use Math::BigInt lib => 'Foo,Math::BigInt::Bar';

Calc.pm uses as internal format an array of elements of some decimal base
(usually 1e5 or 1e7) with the least significant digit first, while BitVect.pm
uses a bit vector of base 2, most significant bit first. Other modules might
use even different means of representing the numbers. See the respective
module documentation for further details.

=head2 SIGN

The sign is either '+', '-', 'NaN', '+inf' or '-inf' and stored seperately.

A sign of 'NaN' is used to represent the result when input arguments are not
numbers or as a result of 0/0. '+inf' and '-inf' represent plus respectively
minus infinity. You will get '+inf' when dividing a positive number by 0, and
'-inf' when dividing any negative number by 0.

=head2 mantissa(), exponent() and parts()

C<mantissa()> and C<exponent()> return the said parts of the BigInt such
that:

        $m = $x->mantissa();
        $e = $x->exponent();
        $y = $m * ( 10 ** $e );
        print "ok\n" if $x == $y;

C<< ($m,$e) = $x->parts() >> is just a shortcut that gives you both of them
in one go. Both the returned mantissa and exponent have a sign.

Currently, for BigInts C<$e> will be always 0, except for NaN, +inf and -inf,
where it will be NaN; and for $x == 0, where it will be 1
(to be compatible with Math::BigFloat's internal representation of a zero as
C<0E1>).

C<$m> will always be a copy of the original number. The relation between $e
and $m might change in the future, but will always be equivalent in a
numerical sense, e.g. $m might get minimized.

=head1 EXAMPLES
 
  use Math::BigInt;

  sub bint { Math::BigInt->new(shift); }

  $x = Math::BigInt->bstr("1234")      	# string "1234"
  $x = "$x";                         	# same as bstr()
  $x = Math::BigInt->bneg("1234");   	# Bigint "-1234"
  $x = Math::BigInt->babs("-12345"); 	# Bigint "12345"
  $x = Math::BigInt->bnorm("-0 00"); 	# BigInt "0"
  $x = bint(1) + bint(2);            	# BigInt "3"
  $x = bint(1) + "2";                	# ditto (auto-BigIntify of "2")
  $x = bint(1);                      	# BigInt "1"
  $x = $x + 5 / 2;                   	# BigInt "3"
  $x = $x ** 3;                      	# BigInt "27"
  $x *= 2;                           	# BigInt "54"
  $x = Math::BigInt->new(0);       	# BigInt "0"
  $x--;                              	# BigInt "-1"
  $x = Math::BigInt->badd(4,5)		# BigInt "9"
  print $x->bsstr();			# 9e+0

Examples for rounding:

  use Math::BigFloat;
  use Test;

  $x = Math::BigFloat->new(123.4567);
  $y = Math::BigFloat->new(123.456789);
  Math::BigFloat->accuracy(4);		# no more A than 4

  ok ($x->copy()->fround(),123.4);	# even rounding
  print $x->copy()->fround(),"\n";	# 123.4
  Math::BigFloat->round_mode('odd');	# round to odd
  print $x->copy()->fround(),"\n";	# 123.5
  Math::BigFloat->accuracy(5);		# no more A than 5
  Math::BigFloat->round_mode('odd');	# round to odd
  print $x->copy()->fround(),"\n";	# 123.46
  $y = $x->copy()->fround(4),"\n";	# A = 4: 123.4
  print "$y, ",$y->accuracy(),"\n";	# 123.4, 4

  Math::BigFloat->accuracy(undef);	# A not important now
  Math::BigFloat->precision(2); 	# P important
  print $x->copy()->bnorm(),"\n";	# 123.46
  print $x->copy()->fround(),"\n";	# 123.46

Examples for converting:

  my $x = Math::BigInt->new('0b1'.'01' x 123);
  print "bin: ",$x->as_bin()," hex:",$x->as_hex()," dec: ",$x,"\n";

=head1 Autocreating constants

After C<use Math::BigInt ':constant'> all the B<integer> decimal, hexadecimal
and binary constants in the given scope are converted to C<Math::BigInt>.
This conversion happens at compile time. 

In particular,

  perl -MMath::BigInt=:constant -e 'print 2**100,"\n"'

prints the integer value of C<2**100>. Note that without conversion of 
constants the expression 2**100 will be calculated as perl scalar.

Please note that strings and floating point constants are not affected,
so that

  	use Math::BigInt qw/:constant/;

	$x = 1234567890123456789012345678901234567890
		+ 123456789123456789;
	$y = '1234567890123456789012345678901234567890'
		+ '123456789123456789';

do not work. You need an explicit Math::BigInt->new() around one of the
operands. You should also quote large constants to protect loss of precision:

	use Math::Bigint;

	$x = Math::BigInt->new('1234567889123456789123456789123456789');

Without the quotes Perl would convert the large number to a floating point
constant at compile time and then hand the result to BigInt, which results in
an truncated result or a NaN.

This also applies to integers that look like floating point constants:

	use Math::BigInt ':constant';

	print ref(123e2),"\n";
	print ref(123.2e2),"\n";

will print nothing but newlines. Use either L<bignum> or L<Math::BigFloat>
to get this to work.

=head1 PERFORMANCE

Using the form $x += $y; etc over $x = $x + $y is faster, since a copy of $x
must be made in the second case. For long numbers, the copy can eat up to 20%
of the work (in the case of addition/subtraction, less for
multiplication/division). If $y is very small compared to $x, the form
$x += $y is MUCH faster than $x = $x + $y since making the copy of $x takes
more time then the actual addition.

With a technique called copy-on-write, the cost of copying with overload could
be minimized or even completely avoided. A test implementation of COW did show
performance gains for overloaded math, but introduced a performance loss due
to a constant overhead for all other operatons.

The rewritten version of this module is slower on certain operations, like
new(), bstr() and numify(). The reason are that it does now more work and
handles more cases. The time spent in these operations is usually gained in
the other operations so that programs on the average should get faster. If
they don't, please contect the author.

Some operations may be slower for small numbers, but are significantly faster
for big numbers. Other operations are now constant (O(1), like bneg(), babs()
etc), instead of O(N) and thus nearly always take much less time. These
optimizations were done on purpose.

If you find the Calc module to slow, try to install any of the replacement
modules and see if they help you. 

=head2 Alternative math libraries

You can use an alternative library to drive Math::BigInt via:

	use Math::BigInt lib => 'Module';

See L<MATH LIBRARY> for more information.

For more benchmark results see L<http://bloodgate.com/perl/benchmarks.html>.

=head2 SUBCLASSING

=head1 Subclassing Math::BigInt

The basic design of Math::BigInt allows simple subclasses with very little
work, as long as a few simple rules are followed:

=over 2

=item *

The public API must remain consistent, i.e. if a sub-class is overloading
addition, the sub-class must use the same name, in this case badd(). The
reason for this is that Math::BigInt is optimized to call the object methods
directly.

=item *

The private object hash keys like C<$x->{sign}> may not be changed, but
additional keys can be added, like C<$x->{_custom}>.

=item *

Accessor functions are available for all existing object hash keys and should
be used instead of directly accessing the internal hash keys. The reason for
this is that Math::BigInt itself has a pluggable interface which permits it
to support different storage methods.

=back

More complex sub-classes may have to replicate more of the logic internal of
Math::BigInt if they need to change more basic behaviors. A subclass that
needs to merely change the output only needs to overload C<bstr()>. 

All other object methods and overloaded functions can be directly inherited
from the parent class.

At the very minimum, any subclass will need to provide it's own C<new()> and can
store additional hash keys in the object. There are also some package globals
that must be defined, e.g.:

  # Globals
  $accuracy = undef;
  $precision = -2;       # round to 2 decimal places
  $round_mode = 'even';
  $div_scale = 40;

Additionally, you might want to provide the following two globals to allow
auto-upgrading and auto-downgrading to work correctly:

  $upgrade = undef;
  $downgrade = undef;

This allows Math::BigInt to correctly retrieve package globals from the 
subclass, like C<$SubClass::precision>.  See t/Math/BigInt/Subclass.pm or
t/Math/BigFloat/SubClass.pm completely functional subclass examples.

Don't forget to 

	use overload;

in your subclass to automatically inherit the overloading from the parent. If
you like, you can change part of the overloading, look at Math::String for an
example.

=head1 UPGRADING

When used like this:

	use Math::BigInt upgrade => 'Foo::Bar';

certain operations will 'upgrade' their calculation and thus the result to
the class Foo::Bar. Usually this is used in conjunction with Math::BigFloat:

	use Math::BigInt upgrade => 'Math::BigFloat';

As a shortcut, you can use the module C<bignum>:

	use bignum;

Also good for oneliners:

	perl -Mbignum -le 'print 2 ** 255'

This makes it possible to mix arguments of different classes (as in 2.5 + 2)
as well es preserve accuracy (as in sqrt(3)).

Beware: This feature is not fully implemented yet.

=head2 Auto-upgrade

The following methods upgrade themselves unconditionally; that is if upgrade
is in effect, they will always hand up their work:

=over 2

=item bsqrt()

=item div()

=item blog()

=back

Beware: This list is not complete.

All other methods upgrade themselves only when one (or all) of their
arguments are of the class mentioned in $upgrade (This might change in later
versions to a more sophisticated scheme):

=head1 BUGS

=over 2

=item Out of Memory!

Under Perl prior to 5.6.0 having an C<use Math::BigInt ':constant';> and 
C<eval()> in your code will crash with "Out of memory". This is probably an
overload/exporter bug. You can workaround by not having C<eval()> 
and ':constant' at the same time or upgrade your Perl to a newer version.

=item Fails to load Calc on Perl prior 5.6.0

Since eval(' use ...') can not be used in conjunction with ':constant', BigInt
will fall back to eval { require ... } when loading the math lib on Perls
prior to 5.6.0. This simple replaces '::' with '/' and thus might fail on
filesystems using a different seperator.  

=back

=head1 CAVEATS

Some things might not work as you expect them. Below is documented what is
known to be troublesome:

=over 1

=item stringify, bstr(), bsstr() and 'cmp'

Both stringify and bstr() now drop the leading '+'. The old code would return
'+3', the new returns '3'. This is to be consistent with Perl and to make
cmp (especially with overloading) to work as you expect. It also solves
problems with Test.pm, it's ok() uses 'eq' internally. 

Mark said, when asked about to drop the '+' altogether, or make only cmp work:

	I agree (with the first alternative), don't add the '+' on positive
	numbers.  It's not as important anymore with the new internal 
	form for numbers.  It made doing things like abs and neg easier,
	but those have to be done differently now anyway.

So, the following examples will now work all as expected:

	use Test;
        BEGIN { plan tests => 1 }
	use Math::BigInt;

	my $x = new Math::BigInt 3*3;
	my $y = new Math::BigInt 3*3;

	ok ($x,3*3);
	print "$x eq 9" if $x eq $y;
	print "$x eq 9" if $x eq '9';
	print "$x eq 9" if $x eq 3*3;

Additionally, the following still works:
	
	print "$x == 9" if $x == $y;
	print "$x == 9" if $x == 9;
	print "$x == 9" if $x == 3*3;

There is now a C<bsstr()> method to get the string in scientific notation aka
C<1e+2> instead of C<100>. Be advised that overloaded 'eq' always uses bstr()
for comparisation, but Perl will represent some numbers as 100 and others
as 1e+308. If in doubt, convert both arguments to Math::BigInt before doing eq:

	use Test;
        BEGIN { plan tests => 3 }
	use Math::BigInt;

	$x = Math::BigInt->new('1e56'); $y = 1e56;
	ok ($x,$y);			# will fail
	ok ($x->bsstr(),$y);		# okay
	$y = Math::BigInt->new($y);
	ok ($x,$y);			# okay

Alternatively, simple use <=> for comparisations, that will get it always
right. There is not yet a way to get a number automatically represented as
a string that matches exactly the way Perl represents it.

=item int()

C<int()> will return (at least for Perl v5.7.1 and up) another BigInt, not a 
Perl scalar:

	$x = Math::BigInt->new(123);
	$y = int($x);				# BigInt 123
	$x = Math::BigFloat->new(123.45);
	$y = int($x);				# BigInt 123

In all Perl versions you can use C<as_number()> for the same effect:

	$x = Math::BigFloat->new(123.45);
	$y = $x->as_number();			# BigInt 123

This also works for other subclasses, like Math::String.

It is yet unlcear whether overloaded int() should return a scalar or a BigInt.

=item length

The following will probably not do what you expect:

	$c = Math::BigInt->new(123);
	print $c->length(),"\n";		# prints 30

It prints both the number of digits in the number and in the fraction part
since print calls C<length()> in list context. Use something like: 
	
	print scalar $c->length(),"\n";		# prints 3 

=item bdiv

The following will probably not do what you expect:

	print $c->bdiv(10000),"\n";

It prints both quotient and remainder since print calls C<bdiv()> in list
context. Also, C<bdiv()> will modify $c, so be carefull. You probably want
to use
	
	print $c / 10000,"\n";
	print scalar $c->bdiv(10000),"\n";  # or if you want to modify $c

instead.

The quotient is always the greatest integer less than or equal to the
real-valued quotient of the two operands, and the remainder (when it is
nonzero) always has the same sign as the second operand; so, for
example,

	  1 / 4  => ( 0, 1)
	  1 / -4 => (-1,-3)
	 -3 / 4  => (-1, 1)
	 -3 / -4 => ( 0,-3)
	-11 / 2  => (-5,1)
	 11 /-2  => (-5,-1)

As a consequence, the behavior of the operator % agrees with the
behavior of Perl's built-in % operator (as documented in the perlop
manpage), and the equation

	$x == ($x / $y) * $y + ($x % $y)

holds true for any $x and $y, which justifies calling the two return
values of bdiv() the quotient and remainder. The only exception to this rule
are when $y == 0 and $x is negative, then the remainder will also be
negative. See below under "infinity handling" for the reasoning behing this.

Perl's 'use integer;' changes the behaviour of % and / for scalars, but will
not change BigInt's way to do things. This is because under 'use integer' Perl
will do what the underlying C thinks is right and this is different for each
system. If you need BigInt's behaving exactly like Perl's 'use integer', bug
the author to implement it ;)

=item infinity handling

Here are some examples that explain the reasons why certain results occur while
handling infinity:

The following table shows the result of the division and the remainder, so that
the equation above holds true. Some "ordinary" cases are strewn in to show more
clearly the reasoning:

	A /  B  =   C,     R so that C *    B +    R =    A
     =========================================================
	5 /   8 =   0,     5 	     0 *    8 +    5 =    5
	0 /   8 =   0,     0	     0 *    8 +    0 =    0
	0 / inf =   0,     0	     0 *  inf +    0 =    0
	0 /-inf =   0,     0	     0 * -inf +    0 =    0
	5 / inf =   0,     5	     0 *  inf +    5 =    5
	5 /-inf =   0,     5	     0 * -inf +    5 =    5
	-5/ inf =   0,    -5	     0 *  inf +   -5 =   -5
	-5/-inf =   0,    -5	     0 * -inf +   -5 =   -5
       inf/   5 =  inf,    0	   inf *    5 +    0 =  inf
      -inf/   5 = -inf,    0      -inf *    5 +    0 = -inf
       inf/  -5 = -inf,    0	  -inf *   -5 +    0 =  inf
      -inf/  -5 =  inf,    0       inf *   -5 +    0 = -inf
	 5/   5 =    1,    0         1 *    5 +    0 =    5
	-5/  -5 =    1,    0         1 *   -5 +    0 =   -5
       inf/ inf =    1,    0         1 *  inf +    0 =  inf
      -inf/-inf =    1,    0         1 * -inf +    0 = -inf
       inf/-inf =   -1,    0        -1 * -inf +    0 =  inf
      -inf/ inf =   -1,    0         1 * -inf +    0 = -inf
	 8/   0 =  inf,    8       inf *    0 +    8 =    8 
       inf/   0 =  inf,  inf       inf *    0 +  inf =  inf 
         0/   0 =  NaN

These cases below violate the "remainder has the sign of the second of the two
arguments", since they wouldn't match up otherwise.

	A /  B  =   C,     R so that C *    B +    R =    A
     ========================================================
      -inf/   0 = -inf, -inf      -inf *    0 +  inf = -inf 
	-8/   0 = -inf,   -8      -inf *    0 +    8 = -8 

=item Modifying and =

Beware of:

        $x = Math::BigFloat->new(5);
        $y = $x;

It will not do what you think, e.g. making a copy of $x. Instead it just makes
a second reference to the B<same> object and stores it in $y. Thus anything
that modifies $x (except overloaded operators) will modify $y, and vice versa.
Or in other words, C<=> is only safe if you modify your BigInts only via
overloaded math. As soon as you use a method call it breaks:

        $x->bmul(2);
        print "$x, $y\n";       # prints '10, 10'

If you want a true copy of $x, use:

        $y = $x->copy();

You can also chain the calls like this, this will make first a copy and then
multiply it by 2:

        $y = $x->copy()->bmul(2);

See also the documentation for overload.pm regarding C<=>.

=item bpow

C<bpow()> (and the rounding functions) now modifies the first argument and
returns it, unlike the old code which left it alone and only returned the
result. This is to be consistent with C<badd()> etc. The first three will
modify $x, the last one won't:

	print bpow($x,$i),"\n"; 	# modify $x
	print $x->bpow($i),"\n"; 	# ditto
	print $x **= $i,"\n";		# the same
	print $x ** $i,"\n";		# leave $x alone 

The form C<$x **= $y> is faster than C<$x = $x ** $y;>, though.

=item Overloading -$x

The following:

	$x = -$x;

is slower than

	$x->bneg();

since overload calls C<sub($x,0,1);> instead of C<neg($x)>. The first variant
needs to preserve $x since it does not know that it later will get overwritten.
This makes a copy of $x and takes O(N), but $x->bneg() is O(1).

With Copy-On-Write, this issue would be gone, but C-o-W is not implemented
since it is slower for all other things.

=item Mixing different object types

In Perl you will get a floating point value if you do one of the following:

	$float = 5.0 + 2;
	$float = 2 + 5.0;
	$float = 5 / 2;

With overloaded math, only the first two variants will result in a BigFloat:

	use Math::BigInt;
	use Math::BigFloat;
	
	$mbf = Math::BigFloat->new(5);
	$mbi2 = Math::BigInteger->new(5);
	$mbi = Math::BigInteger->new(2);

					# what actually gets called:
	$float = $mbf + $mbi;		# $mbf->badd()
	$float = $mbf / $mbi;		# $mbf->bdiv()
	$integer = $mbi + $mbf;		# $mbi->badd()
	$integer = $mbi2 / $mbi;	# $mbi2->bdiv()
	$integer = $mbi2 / $mbf;	# $mbi2->bdiv()

This is because math with overloaded operators follows the first (dominating)
operand, and the operation of that is called and returns thus the result. So,
Math::BigInt::bdiv() will always return a Math::BigInt, regardless whether
the result should be a Math::BigFloat or the second operant is one.

To get a Math::BigFloat you either need to call the operation manually,
make sure the operands are already of the proper type or casted to that type
via Math::BigFloat->new():
	
	$float = Math::BigFloat->new($mbi2) / $mbi;	# = 2.5

Beware of simple "casting" the entire expression, this would only convert
the already computed result:

	$float = Math::BigFloat->new($mbi2 / $mbi);	# = 2.0 thus wrong!

Beware also of the order of more complicated expressions like:

	$integer = ($mbi2 + $mbi) / $mbf;		# int / float => int
	$integer = $mbi2 / Math::BigFloat->new($mbi);	# ditto

If in doubt, break the expression into simpler terms, or cast all operands
to the desired resulting type.

Scalar values are a bit different, since:
	
	$float = 2 + $mbf;
	$float = $mbf + 2;

will both result in the proper type due to the way the overloaded math works.

This section also applies to other overloaded math packages, like Math::String.

One solution to you problem might be L<autoupgrading|upgrading>.

=item bsqrt()

C<bsqrt()> works only good if the result is a big integer, e.g. the square
root of 144 is 12, but from 12 the square root is 3, regardless of rounding
mode.

If you want a better approximation of the square root, then use:

	$x = Math::BigFloat->new(12);
	Math::BigFloat->precision(0);
	Math::BigFloat->round_mode('even');
	print $x->copy->bsqrt(),"\n";		# 4

	Math::BigFloat->precision(2);
	print $x->bsqrt(),"\n";			# 3.46
	print $x->bsqrt(3),"\n";		# 3.464

=item brsft()

For negative numbers in base see also L<brsft|brsft>.

=back

=head1 LICENSE

This program is free software; you may redistribute it and/or modify it under
the same terms as Perl itself.

=head1 SEE ALSO

L<Math::BigFloat> and L<Math::Big> as well as L<Math::BigInt::BitVect>,
L<Math::BigInt::Pari> and  L<Math::BigInt::GMP>.

The package at
L<http://search.cpan.org/search?mode=module&query=Math%3A%3ABigInt> contains
more documentation including a full version history, testcases, empty
subclass files and benchmarks.

=head1 AUTHORS

Original code by Mark Biggar, overloaded interface by Ilya Zakharevich.
Completely rewritten by Tels http://bloodgate.com in late 2000, 2001.

=cut