#!./perl
# From Tom Phoenix <rootbeer@teleport.com> 22 Feb 1997
# Based upon a test script by kgb@ast.cam.ac.uk (Karl Glazebrook)
# Looking for the hints? You're in the right place.
# The hints are near each test, so search for "TEST #", where
# the pound sign is replaced by the number of the test.
# I'd like to include some more robust tests, but anything
# too subtle to be detected here would require a time-consuming
# test. Also, of course, we're here to detect only flaws in Perl;
# if there are flaws in the underlying system rand, that's not
# our responsibility. But if you want better tests, see
# The Art of Computer Programming, Donald E. Knuth, volume 2,
# chapter 3. ISBN 0-201-03822-6 (v. 2)
BEGIN {
chdir "t" if -d "t";
@INC = "../lib" if -d "../lib";
}
use strict;
use Config;
print "1..11\n";
srand; # Shouldn't need this with 5.004...
# But I'll include it now and test for
# whether we needed it later.
my $reps = 1000; # How many times to try rand each time.
# May be changed, but should be over 500.
# The more the better! (But slower.)
sub bits ($) {
# Takes a small integer and returns the number of one-bits in it.
my $total;
my $bits = sprintf "%o", $_[0];
while (length $bits) {
$total += (0,1,1,2,1,2,2,3)[chop $bits]; # Oct to bits
}
$total;
}
# First, let's see whether randbits is set right
{
my($max, $min, $sum); # Characteristics of rand
my($off, $shouldbe); # Problems with randbits
my($dev, $bits); # Number of one bits
my $randbits = $Config{randbits};
$max = $min = rand(1);
for (1..$reps) {
my $n = rand(1);
$sum += $n;
$bits += bits($n * 256); # Don't be greedy; 8 is enough
# It's too many if randbits is less than 8!
# But that should never be the case... I hope.
# Note: If you change this, you must adapt the
# formula for absolute standard deviation, below.
$max = $n if $n > $max;
$min = $n if $n < $min;
}
# Hints for TEST 1
#
# This test checks for one of Perl's most frequent
# mis-configurations. Your system's documentation
# for rand(2) should tell you what value you need
# for randbits. Usually the diagnostic message
# has the right value as well. Just fix it and
# recompile, and you'll usually be fine. (The main
# reason that the diagnostic message might get the
# wrong value is that Config.pm is incorrect.)
#
if ($max <= 0 or $max >= (1 << $randbits)) { # Just in case...
print "not ok 1\n";
print "# This perl was compiled with randbits=$randbits\n";
print "# which is _way_ off. Or maybe your system rand is broken,\n";
print "# or your C compiler can't multiply, or maybe Martians\n";
print "# have taken over your computer. For starters, see about\n";
print "# trying a better value for randbits, probably smaller.\n";
# If that isn't the problem, we'll have
# to put d_martians into Config.pm
print "# Skipping remaining tests until randbits is fixed.\n";
exit;
}
$off = log($max) / log(2); # log2
$off = int($off) + ($off > 0); # Next more positive int
if ($off) {
$shouldbe = $Config{randbits} + $off;
print "not ok 1\n";
print "# This perl was compiled with randbits=$randbits on $^O.\n";
print "# Consider using randbits=$shouldbe instead.\n";
# And skip the remaining tests; they would be pointless now.
print "# Skipping remaining tests until randbits is fixed.\n";
exit;
} else {
print "ok 1\n";
}
# Hints for TEST 2
#
# This should always be true: 0 <= rand(1) < 1
# If this test is failing, something is seriously wrong,
# either in perl or your system's rand function.
#
if ($min < 0 or $max >= 1) { # Slightly redundant...
print "not ok 2\n";
print "# min too low\n" if $min < 0;
print "# max too high\n" if $max >= 1;
} else {
print "ok 2\n";
}
# Hints for TEST 3
#
# This is just a crude test. The average number produced
# by rand should be about one-half. But once in a while
# it will be relatively far away. Note: This test will
# occasionally fail on a perfectly good system!
# See the hints for test 4 to see why.
#
$sum /= $reps;
if ($sum < 0.4 or $sum > 0.6) {
print "not ok 3\n# Average random number is far from 0.5\n";
} else {
print "ok 3\n";
}
# Hints for TEST 4
#
# NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE
# This test will fail .1% of the time on a normal system.
# also
# This test asks you to see these hints 100% of the time!
# NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE
#
# There is probably no reason to be alarmed that
# something is wrong with your rand function. But,
# if you're curious or if you can't help being
# alarmed, keep reading.
#
# This is a less-crude test than test 3. But it has
# the same basic flaw: Unusually distributed random
# values should occasionally appear in every good
# random number sequence. (If you flip a fair coin
# twenty times every day, you'll see it land all
# heads about one time in a million days, on the
# average. That might alarm you if you saw it happen
# on the first day!)
#
# So, if this test failed on you once, run it a dozen
# times. If it keeps failing, it's likely that your
# rand is bogus. If it keeps passing, it's likely
# that the one failure was bogus. If it's a mix,
# read on to see about how to interpret the tests.
#
# The number printed in square brackets is the
# standard deviation, a statistical measure
# of how unusual rand's behavior seemed. It should
# fall in these ranges with these *approximate*
# probabilities:
#
# under 1 68.26% of the time
# 1-2 27.18% of the time
# 2-3 4.30% of the time
# over 3 0.26% of the time
#
# If the numbers you see are not scattered approximately
# (not exactly!) like that table, check with your vendor
# to find out what's wrong with your rand. Or with this
# algorithm. :-)
#
# Calculating absoulute standard deviation for number of bits set
# (eight bits per rep)
$dev = abs ($bits - $reps * 4) / sqrt($reps * 2);
if ($dev < 1.96) {
print "ok 4\n"; # 95% of the time.
print "# Your rand seems fine. If this test failed\n";
print "# previously, you may want to run it again.\n";
} elsif ($dev < 2.575) {
print "ok 4\n# In here about 4% of the time. Hmmm...\n";
print "# This is ok, but suspicious. But it will happen\n";
print "# one time out of 25, more or less.\n";
print "# You should run this test again to be sure.\n";
} elsif ($dev < 3.3) {
print "ok 4\n# In this range about 1% of the time.\n";
print "# This is very suspicious. It will happen only\n";
print "# about one time out of 100, more or less.\n";
print "# You should run this test again to be sure.\n";
} elsif ($dev < 3.9) {
print "not ok 4\n# In this range very rarely.\n";
print "# This is VERY suspicious. It will happen only\n";
print "# about one time out of 1000, more or less.\n";
print "# You should run this test again to be sure.\n";
} else {
print "not ok 4\n# Seriously whacked.\n";
print "# This is VERY VERY suspicious.\n";
print "# Your rand seems to be bogus.\n";
}
print "#\n# If you are having random number troubles,\n";
print "# see the hints within the test script for more\n";
printf "# information on why this might fail. [ %.3f ]\n", $dev;
}
{
srand; # These three lines are for test 7
my $time = time; # It's just faster to do them here.
my $rand = join ", ", rand, rand, rand;
# Hints for TEST 5
#
# This test checks that the argument to srand actually
# sets the seed for generating random numbers.
#
srand(3.14159);
my $r = rand;
srand(3.14159);
if (rand != $r) {
print "not ok 5\n";
print "# srand is not consistent.\n";
} else {
print "ok 5\n";
}
# Hints for TEST 6
#
# This test just checks that the previous one didn't
# give us false confidence!
#
if (rand == $r) {
print "not ok 6\n";
print "# rand is now unchanging!\n";
} else {
print "ok 6\n";
}
# Hints for TEST 7
#
# This checks that srand without arguments gives
# different sequences each time. Note: You shouldn't
# be calling srand more than once unless you know
# what you're doing! But if this fails on your
# system, run perlbug and let the developers know
# what other sources of randomness srand should
# tap into.
#
while ($time == time) { } # Wait for new second, just in case.
srand;
if ((join ", ", rand, rand, rand) eq $rand) {
print "not ok 7\n";
print "# srand without args isn't varying.\n";
} else {
print "ok 7\n";
}
}
# Now, let's see whether rand accepts its argument
{
my($max, $min);
$max = $min = rand(100);
for (1..$reps) {
my $n = rand(100);
$max = $n if $n > $max;
$min = $n if $n < $min;
}
# Hints for TEST 8
#
# This test checks to see that rand(100) really falls
# within the range 0 - 100, and that the numbers produced
# have a reasonably-large range among them.
#
if ($min < 0 or $max >= 100 or ($max - $min) < 65) {
print "not ok 8\n";
print "# min too low\n" if $min < 0;
print "# max too high\n" if $max >= 100;
print "# range too narrow\n" if ($max - $min) < 65;
} else {
print "ok 8\n";
}
# Hints for TEST 9
#
# This test checks that rand without an argument
# is equivalent to rand(1).
#
$_ = 12345; # Just for fun.
srand 12345;
my $r = rand;
srand 12345;
if (rand(1) == $r) {
print "ok 9\n";
} else {
print "not ok 9\n";
print "# rand without arguments isn't rand(1)!\n";
}
# Hints for TEST 10
#
# This checks that rand without an argument is not
# rand($_). (In case somebody got overzealous.)
#
if ($r >= 1) {
print "not ok 10\n";
print "# rand without arguments isn't under 1!\n";
} else {
print "ok 10\n";
}
}
# Hints for TEST 11
#
# This test checks whether Perl called srand for you. This should
# be the case in version 5.004 and later. Note: You must still
# call srand if your code might ever be run on a pre-5.004 system!
#
AUTOSRAND:
{
unless ($Config{d_fork}) {
# Skip this test. It's not likely to be system-specific, anyway.
print "ok 11\n# Skipping this test on this platform.\n";
last;
}
my($pid, $first);
for (1..5) {
my $PERL = (($^O eq 'VMS') ? "MCR $^X"
: ($^O eq 'MSWin32') ? '.\perl'
: './perl');
$pid = open PERL, qq[$PERL -e "print rand"|];
die "Couldn't pipe from perl: $!" unless defined $pid;
if (defined $first) {
if ($first ne <PERL>) {
print "ok 11\n";
last AUTOSRAND;
}
} else {
$first = <PERL>;
}
close PERL or die "perl returned error code $?";
}
print "not ok 11\n# srand isn't being autocalled.\n";
}