| --TEST-- | |
| Bug #75170: mt_rand() bias on 64-bit machines | |
| --CREDITS-- | |
| Solar Designer in https://externals.io/message/100229 | |
| --FILE-- | |
| // PHP pre-7.1.0 modulo bias | |
| mt_srand(1234567890); | |
| $total = 10000; | |
| $max = 0x66666666; | |
| $halves[0] = $halves[1] = 0; | |
| for ($i = 0; $i < $total; $i++) { | |
| $halves[(mt_rand(0, $max - 1) >> 1) & 1]++; | |
| } | |
| printf("%.1f%% vs. %.1f%%\n", 100. * $halves[0] / $total, 100. * $halves[1] / $total); | |
| // PHP 7.1.0 to 7.2.0beta2 modulo bias bug found during work | |
| // on http://www.openwall.com/php_mt_seed/ | |
| mt_srand(1234567890); | |
| $total = 10000; | |
| $max = 0x66666666; | |
| $halves[0] = $halves[1] = 0; | |
| for ($i = 0; $i < $total; $i++) { | |
| $halves[(int) (mt_rand(0, $max - 1) / ($max / 2))]++; | |
| } | |
| printf("%.1f%% vs. %.1f%%\n", 100. * $halves[0] / $total, 100. * $halves[1] / $total); | |
| --EXPECT-- | |
| 49.5% vs. 50.5% | |
| 50.5% vs. 49.5% | |