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In the unlikely event #15

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7dc0761
Try not-too-hard to avoid aborting in benchmarks
tokenrove Aug 22, 2020
9755342
Moderately improve PCG32 seeding without rdrand
tokenrove Aug 22, 2020
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28 changes: 19 additions & 9 deletions c_src/pcg32.c
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Original file line number Diff line number Diff line change
Expand Up @@ -35,26 +35,36 @@
#include "rdtsc.h"
#endif

static __thread uint64_t state = 5573589319906701683ULL;

static uint32_t pcg32(void)
{
uint64_t oldstate = state;
state = oldstate * 6364136223846793005ULL;
uint32_t xorshifted = ((oldstate >> 18u) ^ oldstate) >> 27u;
uint32_t rot = oldstate >> 59u;
uint32_t v = (xorshifted >> rot) | (xorshifted << ((-rot) & 31));
return v;
}

uint32_t uniform32(void)
{
static __thread bool seeded = false;
static __thread uint64_t state;
if (unlikely(!seeded)) {
uint64_t t;
#ifdef HAVE_RDRAND
state = rdrand64();
t = rdrand64();
#else
uint64_t u;
rdtsc(&state, &u);
rdtsc(&t, &u);
#endif
pcg32();
state += t;
pcg32();
seeded = true;
}

uint64_t oldstate = state;
state = oldstate * 6364136223846793005ULL;
uint32_t xorshifted = ((oldstate >> 18u) ^ oldstate) >> 27u;
uint32_t rot = oldstate >> 59u;
uint32_t v = (xorshifted >> rot) | (xorshifted << ((-rot) & 31));
return v;
return pcg32();
}

ERL_NIF_TERM uniform_1(ErlNifEnv *env,
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2 changes: 1 addition & 1 deletion c_src/stub.c
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Original file line number Diff line number Diff line change
Expand Up @@ -50,7 +50,7 @@ int main(void)

int main(void)
{
uint32_t modulus = uniform32();
uint32_t modulus = uniform32() || uniform32();
for (size_t i = 0; i < 10000000UL; ++i)
uniform_1(NULL, 1, (const ERL_NIF_TERM[]){modulus});
return 0;
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