Bug #55519 [Opn->Asn]: mt_rand only generetes even 64 bits numbers

Edit report at https://bugs.php.net/bug.php?id=55519&edit=1 ID: 55519 Updated by: aharvey@php.net Reported by: sergio dot bobillier at gmail dot com Summary: mt_rand only generetes even 64 bits numbers -Status: Open +Status: Assigned Type: Bug Package: Math related Operating System: Linux (Ubuntu 11.04 x64) PHP Version: Irrelevant -Assigned To: +Assigned To: aharvey Block user comment: N Private report: N New Comment: Verified on 64-bit OS X, at least beyond a certain set of mt_rand() bounds. Not entirely sure what those actual bounds are yet. Previous Comments: ------------------------------------------------------------------------ [2011-08-27 09:09:30] sergio dot bobillier at gmail dot com Description: ------------ I was doing a lame RSA implementation when I discovered that mt_rand only generates even numbers when the number is a 64 bits integer. The Test script shows the script I used to generate two 64 bits integers p and q with mt_rand. I was doing primality test only with odd numbers since even numbers are not prime but the script never do the primality test because all the generated numbers are even. I thought this might be an integer overflow problem but I'm doing this on a 64 bits system and the var_dump function shows that the variables are actually integers like so: int(2117698586505379840) int(1690740540401778688) int(3279295862706012160) int(4526730875131396096) int(3188107862534520832) int(1914802535743356928) int(4172596828035874816) int(4559249790717657088) int(1938449129751445504) int(1859647742213619712) Test script: --------------- function is_prime($num) { // See if the number is prime echo "Primality test"; return true; } function gen_keys() { // 1. find two 64 bits primes p and q $p = 0; $q = 0; while(!$p) { $p = mt_rand(72057594037927936, 4611686018427387904); // debugging: var_dump($p); if($p % 2 == 0) { $p = 0; } else { // Primality test in another function // (not important here) echo "odd"; if(!is_prime($p)) $p = 0; } } echo $p; } Expected result: ---------------- I expect the mt_rand to generate some odd numbers and make the script go through the primality test or at least print "odd" Actual result: -------------- The script doesn't reach the primality or print "odd" test because all generated numbers are even. ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=55519&edit=1