What PRNG generator does Godot use?

system · January 3, 2017, 3:44pm


	Attention	Topic was automatically imported from the old Question2Answer platform.
	Asked By	Cameron Kilgore
	Old Version	Published before Godot 3 was released.

I am currently working on a project that involves random operations, and before I go further down the rabbit hole of building a custom RNG within GDScript (based on the Mersenne Twister algorithm), I would like to know what specific PRNG algorithm is used by the GDScript rand() functions, in the hopes that time spent building out MT can be better spent on other functionality. Thanks!

You can edit Godot if you want. There’s even the C code in the Wikipedia:
Mersenne Twister - Wikipedia

mateusak | 2017-01-04 15:28

system · January 3, 2017, 4:08pm


	Reply From:	Zylann

I thought it was the rand() C provides, however it turns out it is a different one:

github.com

godotengine/godot/blob/master/core/math/math_funcs.cpp#L43


      
          #include "core/error/error_macros.h"
          
          RandomPCG Math::default_rand(RandomPCG::DEFAULT_SEED, RandomPCG::DEFAULT_INC);
          
          uint32_t Math::rand_from_seed(uint64_t *seed) {
          	RandomPCG rng = RandomPCG(*seed, RandomPCG::DEFAULT_INC);
          	uint32_t r = rng.rand();
          	*seed = rng.get_seed();
          	return r;
          }
          
          void Math::seed(uint64_t x) {
          	default_rand.seed(x);
          }
          
          void Math::randomize() {
          	default_rand.randomize();
          }
          
          uint32_t Math::rand() {
          	return default_rand.rand();

The title says it’s a Xorshift31 PRNG.

Thanks for clarifying! Xorshift31 is more than sufficient enough for what my needs entail.

Cameron Kilgore | 2017-01-19 14:00

It was recently changed to XSH-RR: Replace the existing PRNG (Xorshift31) with (minimal) PCG (XSH-RR var… · godotengine/godot@4c90046 · GitHub

Zylann | 2017-01-19 19:20