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make t/op/rand.t fail less often
[perl5.git] / t / op / rand.t
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1#!./perl
2
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3# From Tom Phoenix <rootbeer@teleport.com> 22 Feb 1997
4# Based upon a test script by kgb@ast.cam.ac.uk (Karl Glazebrook)
a0d0e21e 5
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6# Looking for the hints? You're in the right place.
7# The hints are near each test, so search for "TEST #", where
8# the pound sign is replaced by the number of the test.
a0d0e21e 9
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10# I'd like to include some more robust tests, but anything
11# too subtle to be detected here would require a time-consuming
12# test. Also, of course, we're here to detect only flaws in Perl;
13# if there are flaws in the underlying system rand, that's not
14# our responsibility. But if you want better tests, see
15# The Art of Computer Programming, Donald E. Knuth, volume 2,
16# chapter 3. ISBN 0-201-03822-6 (v. 2)
a0d0e21e 17
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18BEGIN {
19 chdir "t" if -d "t";
69026470 20 @INC = qw(. ../lib);
748a9306 21}
748a9306 22
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23use strict;
24use Config;
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25
26require "test.pl";
27plan(tests => 8);
3524d3b9 28
ec761cee 29
5b35fc8b 30my $reps = 15000; # How many times to try rand each time.
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31 # May be changed, but should be over 500.
32 # The more the better! (But slower.)
33
34sub bits ($) {
35 # Takes a small integer and returns the number of one-bits in it.
36 my $total;
37 my $bits = sprintf "%o", $_[0];
38 while (length $bits) {
39 $total += (0,1,1,2,1,2,2,3)[chop $bits]; # Oct to bits
40 }
41 $total;
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42}
43
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44# First, let's see whether randbits is set right
45{
46 my($max, $min, $sum); # Characteristics of rand
47 my($off, $shouldbe); # Problems with randbits
48 my($dev, $bits); # Number of one bits
49 my $randbits = $Config{randbits};
50 $max = $min = rand(1);
51 for (1..$reps) {
52 my $n = rand(1);
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53 if ($n < 0.0 or $n >= 1.0) {
54 print <<EOM;
55# WHOA THERE! \$Config{drand01} is set to '$Config{drand01}',
56# but that apparently produces values < 0.0 or >= 1.0.
57# Make sure \$Config{drand01} is a valid expression in the
58# C-language, and produces values in the range [0.0,1.0).
59#
60# I give up.
61EOM
62 exit;
63 }
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64 $sum += $n;
65 $bits += bits($n * 256); # Don't be greedy; 8 is enough
66 # It's too many if randbits is less than 8!
67 # But that should never be the case... I hope.
68 # Note: If you change this, you must adapt the
69 # formula for absolute standard deviation, below.
70 $max = $n if $n > $max;
71 $min = $n if $n < $min;
72 }
73
74
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75 # This test checks for one of Perl's most frequent
76 # mis-configurations. Your system's documentation
77 # for rand(2) should tell you what value you need
78 # for randbits. Usually the diagnostic message
79 # has the right value as well. Just fix it and
80 # recompile, and you'll usually be fine. (The main
81 # reason that the diagnostic message might get the
82 # wrong value is that Config.pm is incorrect.)
83 #
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84 unless (ok( !$max <= 0 or $max >= (2 ** $randbits))) {# Just in case...
85 print <<DIAG;
86# max=[$max] min=[$min]
87# This perl was compiled with randbits=$randbits
88# which is _way_ off. Or maybe your system rand is broken,
89# or your C compiler can't multiply, or maybe Martians
90# have taken over your computer. For starters, see about
91# trying a better value for randbits, probably smaller.
92DIAG
93
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94 # If that isn't the problem, we'll have
95 # to put d_martians into Config.pm
96 print "# Skipping remaining tests until randbits is fixed.\n";
97 exit;
98 }
99
100 $off = log($max) / log(2); # log2
101 $off = int($off) + ($off > 0); # Next more positive int
9be67dbc 102 unless (is( $off, 0 )) {
ec761cee 103 $shouldbe = $Config{randbits} + $off;
9be67dbc 104 print "# max=[$max] min=[$min]\n";
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105 print "# This perl was compiled with randbits=$randbits on $^O.\n";
106 print "# Consider using randbits=$shouldbe instead.\n";
107 # And skip the remaining tests; they would be pointless now.
108 print "# Skipping remaining tests until randbits is fixed.\n";
109 exit;
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110 }
111
9be67dbc 112
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113 # This should always be true: 0 <= rand(1) < 1
114 # If this test is failing, something is seriously wrong,
115 # either in perl or your system's rand function.
116 #
9be67dbc 117 unless (ok( !($min < 0 or $max >= 1) )) { # Slightly redundant...
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118 print "# min too low\n" if $min < 0;
119 print "# max too high\n" if $max >= 1;
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120 }
121
9be67dbc 122
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123 # This is just a crude test. The average number produced
124 # by rand should be about one-half. But once in a while
125 # it will be relatively far away. Note: This test will
126 # occasionally fail on a perfectly good system!
127 # See the hints for test 4 to see why.
128 #
129 $sum /= $reps;
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130 unless (ok( !($sum < 0.4 or $sum > 0.6) )) {
131 print "# Average random number is far from 0.5\n";
ec761cee 132 }
a0d0e21e 133
9be67dbc 134
ec761cee 135 # NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE
81b6403e 136 # This test will fail .006% of the time on a normal system.
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137 # also
138 # This test asks you to see these hints 100% of the time!
139 # NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE
140 #
141 # There is probably no reason to be alarmed that
142 # something is wrong with your rand function. But,
143 # if you're curious or if you can't help being
144 # alarmed, keep reading.
145 #
146 # This is a less-crude test than test 3. But it has
147 # the same basic flaw: Unusually distributed random
148 # values should occasionally appear in every good
149 # random number sequence. (If you flip a fair coin
150 # twenty times every day, you'll see it land all
151 # heads about one time in a million days, on the
152 # average. That might alarm you if you saw it happen
153 # on the first day!)
154 #
155 # So, if this test failed on you once, run it a dozen
156 # times. If it keeps failing, it's likely that your
157 # rand is bogus. If it keeps passing, it's likely
158 # that the one failure was bogus. If it's a mix,
159 # read on to see about how to interpret the tests.
160 #
161 # The number printed in square brackets is the
162 # standard deviation, a statistical measure
163 # of how unusual rand's behavior seemed. It should
164 # fall in these ranges with these *approximate*
165 # probabilities:
166 #
167 # under 1 68.26% of the time
168 # 1-2 27.18% of the time
169 # 2-3 4.30% of the time
170 # over 3 0.26% of the time
171 #
172 # If the numbers you see are not scattered approximately
173 # (not exactly!) like that table, check with your vendor
174 # to find out what's wrong with your rand. Or with this
175 # algorithm. :-)
176 #
93f09d7b 177 # Calculating absolute standard deviation for number of bits set
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178 # (eight bits per rep)
179 $dev = abs ($bits - $reps * 4) / sqrt($reps * 2);
748a9306 180
81b6403e 181 ok( $dev < 4.0 );
9be67dbc 182
ec761cee 183 if ($dev < 1.96) {
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184 print "# Your rand seems fine. If this test failed\n";
185 print "# previously, you may want to run it again.\n";
186 } elsif ($dev < 2.575) {
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187 print "# This is ok, but suspicious. But it will happen\n";
188 print "# one time out of 25, more or less.\n";
189 print "# You should run this test again to be sure.\n";
190 } elsif ($dev < 3.3) {
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191 print "# This is very suspicious. It will happen only\n";
192 print "# about one time out of 100, more or less.\n";
193 print "# You should run this test again to be sure.\n";
194 } elsif ($dev < 3.9) {
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195 print "# This is VERY suspicious. It will happen only\n";
196 print "# about one time out of 1000, more or less.\n";
197 print "# You should run this test again to be sure.\n";
198 } else {
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199 print "# This is VERY VERY suspicious.\n";
200 print "# Your rand seems to be bogus.\n";
201 }
202 print "#\n# If you are having random number troubles,\n";
203 print "# see the hints within the test script for more\n";
204 printf "# information on why this might fail. [ %.3f ]\n", $dev;
748a9306 205}
748a9306 206
a0d0e21e 207
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208# Now, let's see whether rand accepts its argument
209{
210 my($max, $min);
211 $max = $min = rand(100);
212 for (1..$reps) {
213 my $n = rand(100);
214 $max = $n if $n > $max;
215 $min = $n if $n < $min;
216 }
217
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218 # This test checks to see that rand(100) really falls
219 # within the range 0 - 100, and that the numbers produced
220 # have a reasonably-large range among them.
221 #
9be67dbc 222 unless ( ok( !($min < 0 or $max >= 100 or ($max - $min) < 65) ) ) {
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223 print "# min too low\n" if $min < 0;
224 print "# max too high\n" if $max >= 100;
225 print "# range too narrow\n" if ($max - $min) < 65;
ec761cee 226 }
3524d3b9 227
9be67dbc 228
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229 # This test checks that rand without an argument
230 # is equivalent to rand(1).
231 #
232 $_ = 12345; # Just for fun.
233 srand 12345;
234 my $r = rand;
235 srand 12345;
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236 is(rand(1), $r, 'rand() without args is rand(1)');
237
748a9306 238
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239 # This checks that rand without an argument is not
240 # rand($_). (In case somebody got overzealous.)
241 #
9be67dbc 242 ok($r < 1, 'rand() without args is under 1');
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243}
244