Re: mt_rand() - the same forever?

Janek schreef: > On Sun, Oct 5, 2008 at 10:05 PM, Ashley Sheridan > <ash@ashleysheridan.co.uk> wrote: >> On Sun, 2008-10-05 at 21:57 +0200, Janek wrote: >>> I know, but I *want* to seed it. My goal is to have a fixed >>> pseudorandom sequence for each integer (seed) and I don't want those >>> sequences to change regarding PHP version. >>> >>> Janek >>> >>> On Sun, Oct 5, 2008 at 9:52 PM, Richard Heyes <richard@php.net> wrote: >>>>> I wonder whether I can rely on the stability of mt_srand() and >>>>> mt_rand(). I want them to generate the same sequence for a fixed seed, >>>>> regardless of PHP version. Do you think I can trust it? >>>>> Janek >>>> Keep in mind (if you're not already) that mt_rand() doesn't >>>> technically need to be seeded. >>>> >>>> -- >>>> Richard Heyes >>>> >>>> HTML5 Graphing for FF, Chrome, Opera and Safari: >>>> http://www.phpguru.org/RGraph >>>> >> Doesn't it also rely on the system clock as well? >> >> >> Ash >> www.ashleysheridan.co.uk >> >> > > No. When I give a fixed seed to mt_srand(), each time I get the same > sequence of mt_rand()s. My question is wheather the actual algorithm > behind these functions is likely to change in the next version of PHP > or not. not likely to change in the next version at all. but there is no guarantee that somewhere down the road a new 'rand' algorythm won't be used either, 3 things to consider doing: 1. write your own php extension that copies the mt_srand() function as it is now and use your extension's version of the function ... then you can be sure it won't change. 2. ask the devs on internals@lists.php.net what they think the likelyhood is that the output may change in the future. 3. pre-generate the sequences and store them, then use those pre-generated sequences instead of using mt_srand() (obviously this may not be viable at all) > > Janek >