head	1.1;access;symbols	zero-five-zero:1.1	zero-four-seventeen:1.1	zero-four-ten:1.1	zero-four-nine:1.1	zero-four-eight:1.1	zero-four-five:1.1	zero-four-three:1.1	zero-four-zero:1.1;locks	neto:1.1;comment	@# @;1.1date	97.11.01.22.17.43;	author neto;	state Exp;branches;next	;desc@A Perl version of the Stanford GraphBase random number generator.@1.1log@Initial revision@text@#! @@PERL@@ -w# @@configure_input@@# This is a Perl version of the Stanford GraphBase random number generator.# This file is *not* part of the Stanford GraphBase.# This file is in the public domain, and comes with no warranty.# David Neto, November 1, 1997.use strict;my (@@A);my ($ptr);sub gb_flip_initialize {	@@A=(-1);}sub gb_mod_diff {	my ($x,$y) = @@_;	return ($x-$y) & 0x7fffffff;}sub gb_flip_cycle {	my ($j, $i);	for $j (32..55) { $A[$j-31] = &gb_mod_diff($A[$j-31],$A[$j]   ); }	for $i (25..55) { $A[$i]    = &gb_mod_diff($A[$i],   $A[$i-24]); }	$ptr = 54;	return $A[55];}sub gb_next_rand {	return $A[$ptr] >= 0 ? $A[$ptr--] : &gb_flip_cycle;}sub gb_init_rand {	my ($seed) = shift;	my ($i, $prev, $next);	&gb_flip_initialize;	$next = 1;	$seed = $prev = &gb_mod_diff($seed,0);	$A[55] = $prev;	for ( $i=21; $i ; $i = ($i+21) % 55) {		$A[$i] = $next;		# Section 9: Compute a new next value, based on next, prev, and seed.		$next = &gb_mod_diff($prev, $next);		if ( $seed & 1 ) {$seed = 0x40000000 + ($seed >> 1);}		else {$seed >>= 1;}		$next = &gb_mod_diff($next,$seed);		# :9		$prev = $A[$i];	}	# Section 8: Get the array values warmed up.	&gb_flip_cycle;	&gb_flip_cycle;	&gb_flip_cycle;	&gb_flip_cycle;	&gb_flip_cycle;	# :8}sub gb_unif_rand {	my ($m, $r, $t);	# Make sure the argument is small enough, and positive.	$m = int( shift ) & 0x7fffffff;	$t = 0x80000000 - (0x80000000 % $m);	do {		$r = &gb_next_rand;	} while ( $t <= $r );	return $r % $m;}sub gb_test {	my ($j);	&gb_init_rand(-314159);	&gb_next_rand == 119318998 || die("Failure on the first try!");	for $j (1..133) { &gb_next_rand; }	&gb_unif_rand(0x55555555) == 748103812 || die("Failure on the second try!");	print STDERR "Ok the gb_flip routines seem to work!\n";	return 0;}# &gb_test;@