#40724 [Bgs->Opn]: srand returns different results in 5.2.1 than in previous versions

ID: 40724 Updated by: chagenbu@php.net Reported By: dave at dmorg dot org -Status: Bogus +Status: Open Bug Type: Math related Operating System: linux, windows PHP Version: 5.2.1 New Comment: Except that you can, if you pass it the same seed. Mersenne Twister is still a psuedo-random system; same seed should generate the same output. This is a subtle but non-trivial change for people generating psuedo-cryptographic sequences. (Ilia, don't tell me that MT isn't cryptographically secure, of course it's not - that's not the point). Previous Comments: ------------------------------------------------------------------------ [2007-03-05 23:57:53] iliaa@php.net Thank you for taking the time to write to us, but this is not a bug. Please double-check the documentation available at http://www.php.net/manual/ and the instructions on how to report a bug at http://bugs.php.net/how-to-report.php Random numbers are random, so you can't expect to get the same number out of a random number generator. ------------------------------------------------------------------------ [2007-03-05 07:52:38] dave at dmorg dot org Description: ------------ I use srand to seed random numbers with student id numbers so that whenever students relog in to an assignment, their questions have the same input values and they can continue where they left off. I am now getting different results than before. I'm not sure whether this is an unintended consequence of some apparently unrelated code change or whether it is intended. Reproduce code: --------------- <?php mt_srand(42); echo mt_rand(); ?> produces 1387371436 under 4.*, 5.1.1. 5.1.4 produces 1354439493 under 5.2.1 Expected result: ---------------- I would expect results from the random number generator to be consistent when seeded with the same number Actual result: -------------- produces 1387371436 under 4.*, 5.1.1. 5.1.4 produces 1354439493 under 5.2.1 ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=40724&edit=1