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[util] Add mtwist float random number functions

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mtwist_rand_0_1 produces numbers in the range [0, 1) and
mtwist_rand_m1_1 produces numbers in the range (-1, 1). The numbers will
not be denormal, so the distribution should be fairly uniform (as much
as Mersenne Twister itself is), but this needs proper testing.

0 is included for the mtwist_rand_0_1 as it seems useful, but -1 is not
included in mtwist_rand_m1_1 in order to keep the extremes of the
distribution balanced around 0.
This commit is contained in:
Bill Currie 2021-12-22 00:01:26 +09:00
parent 6411518603
commit 91a686d1f5
2 changed files with 41 additions and 0 deletions
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40
include/QF/mersenne.h
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@ -42,5 +42,45 @@ typedef struct {
void mtwist_seed (mtstate_t *state, uint32_t seed);
uint32_t mtwist_rand (mtstate_t *state);
GNU89INLINE inline float mtwist_rand_0_1 (mtstate_t *state);
GNU89INLINE inline float mtwist_rand_m1_1 (mtstate_t *state);
#ifndef IMPLEMENT_MTWIST_Funcs
GNU89INLINE inline
#else
VISIBLE
#endif
float
mtwist_rand_0_1 (mtstate_t *state)
{
union {
uint32_t u;
float f;
} uf;
uf.u = mtwist_rand (state) & 0x007fffff;
uf.u |= 0x3f800000;
return uf.f - 1.0;
}
#ifndef IMPLEMENT_MTWIST_Funcs
GNU89INLINE inline
#else
VISIBLE
#endif
float
mtwist_rand_m1_1 (mtstate_t *state)
{
union {
uint32_t u;
float f;
} uf;
do {
uf.u = mtwist_rand (state) & 0x007fffff;
} while (!uf.u);
uf.u |= 0x40000000;
return uf.f - 3.0;
}
#endif//__QF_mersenne_h

1
libs/util/mersenne.c
View file

@ -48,6 +48,7 @@
There were no differences.
*/
#define IMPLEMENT_MTWIST_Funcs
#include "QF/mersenne.h"
#define KNUTH_MULT 1812433253ul // 0x6c078965