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srand() and rand() portability

Started by Vexorian Apr 15, 2006 at 7:15 AM 5 replies 2.4k views

Original Post

Apr 15, 2006 at 7:15 AM

Of course they are standards so they are available where sdtio is but I was thinking on adding replays to my game, the only problem is that some objects, specially the monsters' AI rely on random numbers. So the question is : would equal srand() values generate the same results for rand() in different platforms? and if not, is there a library that allows this?

smart_idiot

Apr 15, 2006 at 7:18 AM

No, they don't.

Mersenne Twister gets my vote as an alternative.

Anon Mike

Apr 15, 2006 at 1:20 PM

If you're using C++ then boost::random is probably the place to go.

Catafriggm

Apr 15, 2006 at 1:34 PM

I personally like ISAAC best.

Vexorian

Apr 15, 2006 at 6:55 PM

thanks very much with 3 alternatives I guess I have plenty of options

iMalc

Apr 15, 2006 at 7:08 PM

You could easily just obtain and use the code for a common prng, and explicitly use that instead:

//In .cpplong holdrand;//In .hppextern long holdrand;inline void srand(long seed){	holdrand = seed;}inline int rand(void){	return (((holdrand = holdrand * 214013L + 2531011L) >> 16) & 0x7fff);}

I'm not going to pretend it is the best prng in the world, but it is usually good enough (and very fast), and it is probably identical to what you are already using.

etothex

Apr 16, 2006 at 1:38 AM

I vote for boost::random, too. Remember that rand() and other implementations like iMalcs aren't reentrant, so for multi-threaded apps they should be avoided anyway.

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