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Replace the existing PRNG (Xorshift31) with (minimal) PCG (XSH-RR variant with 32-bit output, 64-bit state).

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PCG is better than many alternatives by many metrics (see www.pcg-random.org) including statistical quality with good speed.
This commit is contained in:
Ferenc Arn
2017-01-14 23:34:51 -06:00
parent 5dde810aa5
commit 4c9004671a
7 changed files with 54 additions and 25 deletions
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25
core/math/math_funcs.cpp
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@@ -31,8 +31,9 @@
#include "core/os/os.h"
#include "float.h"
uint32_t Math::default_seed=1;
#include "pcg.h"
pcg32_random_t Math::default_pcg = {1, PCG_DEFAULT_INC_64};
#define PHI 0x9e3779b9
@@ -40,28 +41,26 @@ uint32_t Math::default_seed=1;
static uint32_t Q[4096];
#endif
uint32_t Math::rand_from_seed(uint32_t *seed) {
// Xorshift31 PRNG
if ( *seed == 0 ) *seed = Math::RANDOM_MAX;
(*seed) ^= (*seed) << 13;
(*seed) ^= (*seed) >> 17;
(*seed) ^= (*seed) << 5;
return (*seed) & Math::RANDOM_MAX;
// TODO: we should eventually expose pcg.inc too
uint32_t Math::rand_from_seed(uint64_t *seed) {
pcg32_random_t pcg = {*seed, PCG_DEFAULT_INC_64};
uint32_t r = pcg32_random_r(&pcg);
*seed = pcg.state;
return r;
}
void Math::seed(uint32_t x) {
default_seed=x;
void Math::seed(uint64_t x) {
default_pcg.state=x;
}
void Math::randomize() {
OS::Time time = OS::get_singleton()->get_time();
seed(OS::get_singleton()->get_ticks_usec()*(time.hour+1)*(time.min+1)*(time.sec+1)*rand()); /* *OS::get_singleton()->get_time().sec); // windows doesn't have get_time(), returns always 0 */
seed(OS::get_singleton()->get_ticks_usec()*(time.hour+1)*(time.min+1)*(time.sec+1)*rand()); // TODO: can be simplified.
}
uint32_t Math::rand() {
return rand_from_seed(&default_seed);
return pcg32_random_r(&default_pcg);
}
double Math::randf() {