note 105452 added to function.rand

rand() has a granularity of getrandmax() which means that if you're on a Windows system where getrandmax()==32767 then specifying a range greater than 0-32767 will still only give 32768 unique values. Specifying min=0 and max > getrandmax()+1 where max == 2^n or max == 2^n-1 will return numbers that are multiples of some 2^m where (getrandmax()+1) * 2^m == 2^n. <?php function gcd($x, $y) { // If gmp_gcd() is not available for (;;) { if ($x == 0) return $y; else $y %= $x; if ($y == 0) return $x; else $x %= $y; } } //$rand_max = 0xFFFFFE; // This gives 1 $rand_max = 0xFFFFFF; // This gives 512 $rand_max = 0x1000000; // This gives 512 //$rand_max = 0x1000001; // This gives 1 $gcd = rand(0, $rand_max); for ($i = 0; $i < 1000; ++$i) { $gcd = gcd($gcd, rand(0, $rand_max)); } print($gcd); ?> I would suggest always using mt_rand() instead as a good habit to get into. ---- Server IP: 117.55.229.1 Probable Submitter: 114.75.190.57 ---- Manual Page -- http://www.php.net/manual/en/function.rand.php Edit -- https://master.php.net/note/edit/105452 Del: integrated -- https://master.php.net/note/delete/105452/integrated Del: useless -- https://master.php.net/note/delete/105452/useless Del: bad code -- https://master.php.net/note/delete/105452/bad+code Del: spam -- https://master.php.net/note/delete/105452/spam Del: non-english -- https://master.php.net/note/delete/105452/non-english Del: in docs -- https://master.php.net/note/delete/105452/in+docs Del: other reasons-- https://master.php.net/note/delete/105452 Reject -- https://master.php.net/note/reject/105452 Search -- https://master.php.net/manage/user-notes.php