Merge pull request #43184 from Chaosus/fix_randi_range_biased

Fix biased output of randi_range
This commit is contained in:
Rémi Verschelde 2020-10-30 15:00:44 +01:00 committed by GitHub
commit f98db723b9
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4 changed files with 26 additions and 5 deletions

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@ -58,12 +58,18 @@ public:
_FORCE_INLINE_ real_t randfn(real_t mean = 0.0, real_t deviation = 1.0) { return randbase.randfn(mean, deviation); }
_FORCE_INLINE_ int randi_range(int from, int to) {
unsigned int ret = randbase.rand();
if (to < from) {
return ret % (from - to + 1) + to;
} else {
return ret % (to - from + 1) + from;
int range;
int min;
if (to > from) {
range = to - from + 1;
min = from;
} else if (to < from) {
range = from - to + 1;
min = to;
} else { // from == to
return from;
}
return randbase.rand(range) + min;
}
RandomNumberGenerator() {}

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@ -81,6 +81,10 @@ public:
current_seed = pcg.state;
return pcg32_random_r(&pcg);
}
_FORCE_INLINE_ uint32_t rand(uint32_t bounds) {
current_seed = pcg.state;
return pcg32_boundedrand_r(&pcg, bounds);
}
// Obtaining floating point numbers in [0, 1] range with "good enough" uniformity.
// These functions sample the output of rand() as the fraction part of an infinite binary number,

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@ -23,3 +23,13 @@ void pcg32_srandom_r(pcg32_random_t* rng, uint64_t initstate, uint64_t initseq)
rng->state += initstate;
pcg32_random_r(rng);
}
// Source from https://github.com/imneme/pcg-c-basic/blob/master/pcg_basic.c
uint32_t pcg32_boundedrand_r(pcg32_random_t *rng, uint32_t bound) {
uint32_t threshold = -bound % bound;
for (;;) {
uint32_t r = pcg32_random_r(rng);
if (r >= threshold)
return r % bound;
}
}

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@ -11,5 +11,6 @@
typedef struct { uint64_t state; uint64_t inc; } pcg32_random_t;
uint32_t pcg32_random_r(pcg32_random_t* rng);
void pcg32_srandom_r(pcg32_random_t* rng, uint64_t initstate, uint64_t initseq);
uint32_t pcg32_boundedrand_r(pcg32_random_t* rng, uint32_t bound);
#endif // RANDOM_H