path: root/t/op/rand.t

#!./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 ($max <= 0) {	# Just in case...
	print "not ok 1\n";
	print "# This perl was compiled with randbits=$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.\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 = 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 (rand == $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) {
	$pid = open PERL, "./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";
}