X-Git-Url: https://perl5.git.perl.org/perl5.git/blobdiff_plain/47f6b1df3e028ac6a813ea58707e6a92837c0659..042560a65fd56038b3116f30639cb99d98c48622:/lib/integer.pm

diff --git a/lib/integer.pm b/lib/integer.pm
index f6be58a..caa1ea6 100644
--- a/lib/integer.pm
+++ b/lib/integer.pm
@@ -1,8 +1,10 @@
 package integer;
 
+our $VERSION = '1.00';
+
 =head1 NAME
 
-integer - Perl pragma to compute arithmetic in integer instead of double
+integer - Perl pragma to use integer arithmetic instead of floating point
 
 =head1 SYNOPSIS
 
@@ -12,43 +14,80 @@ integer - Perl pragma to compute arithmetic in integer instead of double
 
 =head1 DESCRIPTION
 
-This tells the compiler to use integer operations
-from here to the end of the enclosing BLOCK.  On many machines, 
-this doesn't matter a great deal for most computations, but on those 
-without floating point hardware, it can make a big difference.
-
-Note that this affects the operations, not the numbers.  If you run this
-code
+This tells the compiler to use integer operations from here to the end
+of the enclosing BLOCK.  On many machines, this doesn't matter a great
+deal for most computations, but on those without floating point
+hardware, it can make a big difference in performance.
+
+Note that this only affects how most of the arithmetic and relational
+B<operators> handle their operands and results, and B<not> how all
+numbers everywhere are treated.  Specifically, C<use integer;> has the
+effect that before computing the results of the arithmetic operators
+(+, -, *, /, %, +=, -=, *=, /=, %=, and unary minus), the comparison
+operators (<, <=, >, >=, ==, !=, <=>), and the bitwise operators (|, &,
+^, <<, >>, |=, &=, ^=, <<=, >>=), the operands have their fractional
+portions truncated (or floored), and the result will have its
+fractional portion truncated as well.  In addition, the range of
+operands and results is restricted to that of familiar two's complement
+integers, i.e., -(2**31) .. (2**31-1) on 32-bit architectures, and
+-(2**63) .. (2**63-1) on 64-bit architectures.  For example, this code
 
     use integer;
-    $x = 1.5;
-    $y = $x + 1;
-    $z = -1.5;
-
-you'll be left with C<$x == 1.5>, C<$y == 2> and C<$z == -1>.  The $z
-case happens because unary C<-> counts as an operation.
-
-Native integer arithmetic (as provided by your C compiler) is used.
-This means that Perl's own semantics for arithmetic operations may
-not be preserved.  One common source of trouble is the modulus of
-negative numbers, which Perl does one way, but your hardware may do
-another.
-
-  % perl -le 'print (4 % -3)'
-  -2
-  % perl -Minteger -le 'print (4 % -3)'
-  1
-
-See L<perlmod/Pragmatic Modules>.
+    $x = 5.8;
+    $y = 2.5;
+    $z = 2.7;
+    $a = 2**31 - 1;  # Largest positive integer on 32-bit machines
+    $, = ", ";
+    print $x, -$x, $x + $y, $x - $y, $x / $y, $x * $y, $y == $z, $a, $a + 1;
+
+will print:  5.8, -5, 7, 3, 2, 10, 1, 2147483647, -2147483648
+
+Note that $x is still printed as having its true non-integer value of
+5.8 since it wasn't operated on.  And note too the wrap-around from the
+largest positive integer to the largest negative one.   Also, arguments
+passed to functions and the values returned by them are B<not> affected
+by C<use integer;>.  E.g.,
+
+    srand(1.5);
+    $, = ", ";
+    print sin(.5), cos(.5), atan2(1,2), sqrt(2), rand(10);
+
+will give the same result with or without C<use integer;>  The power
+operator C<**> is also not affected, so that 2 ** .5 is always the
+square root of 2.  Now, it so happens that the pre- and post- increment
+and decrement operators, ++ and --, are not affected by C<use integer;>
+either.  Some may rightly consider this to be a bug -- but at least it's
+a long-standing one.
+
+Finally, C<use integer;> also has an additional affect on the bitwise
+operators.  Normally, the operands and results are treated as
+B<unsigned> integers, but with C<use integer;> the operands and results
+are B<signed>.  This means, among other things, that ~0 is -1, and -2 &
+-5 is -6.
+
+Internally, native integer arithmetic (as provided by your C compiler)
+is used.  This means that Perl's own semantics for arithmetic
+operations may not be preserved.  One common source of trouble is the
+modulus of negative numbers, which Perl does one way, but your hardware
+may do another.
+
+    % perl -le 'print (4 % -3)'
+    -2
+    % perl -Minteger -le 'print (4 % -3)'
+    1
+
+See L<perlmodlib/"Pragmatic Modules">, L<perlop/"Integer Arithmetic">
 
 =cut
 
+$integer::hint_bits = 0x1;
+
 sub import {
-    $^H |= 1;
+    $^H |= $integer::hint_bits;
 }
 
 sub unimport {
-    $^H &= ~1;
+    $^H &= ~$integer::hint_bits;
 }
 
 1;