diff options
Diffstat (limited to 'libgfortran/intrinsics/random.c')
| -rw-r--r-- | libgfortran/intrinsics/random.c | 49 |
1 files changed, 20 insertions, 29 deletions
diff --git a/libgfortran/intrinsics/random.c b/libgfortran/intrinsics/random.c index 234c5ff95fd..4a40ce454ed 100644 --- a/libgfortran/intrinsics/random.c +++ b/libgfortran/intrinsics/random.c @@ -272,30 +272,19 @@ jump (xorshift1024star_state* rs) } -/* Super-simple LCG generator used in getosrandom () if /dev/urandom - doesn't exist. */ +/* Splitmix64 recommended by xorshift author for initializing. After + getting one uint64_t value from the OS, this is used to fill in the + rest of the state. */ -#define M 2147483647 /* 2^31 - 1 (A large prime number) */ -#define A 16807 /* Prime root of M, passes statistical tests and produces a full cycle */ -#define Q 127773 /* M / A (To avoid overflow on A * seed) */ -#define R 2836 /* M % A (To avoid overflow on A * seed) */ - -__attribute__((unused)) static uint32_t -lcg_parkmiller(uint32_t seed) +static uint64_t +splitmix64 (uint64_t x) { - uint32_t hi = seed / Q; - uint32_t lo = seed % Q; - int32_t test = A * lo - R * hi; - if (test <= 0) - test += M; - return test; + uint64_t z = (x += 0x9e3779b97f4a7c15); + z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9; + z = (z ^ (z >> 27)) * 0x94d049bb133111eb; + return z ^ (z >> 31); } -#undef M -#undef A -#undef Q -#undef R - /* Get some random bytes from the operating system in order to seed the PRNG. */ @@ -326,7 +315,7 @@ getosrandom (void *buf, size_t buflen) close (fd); return res; } - uint32_t seed = 1234567890; + uint64_t seed = 0x047f7684e9fc949dULL; time_t secs; long usecs; if (gf_gettime (&secs, &usecs) == 0) @@ -338,13 +327,9 @@ getosrandom (void *buf, size_t buflen) pid_t pid = getpid(); seed ^= pid; #endif - uint32_t* ub = buf; - for (size_t i = 0; i < buflen / sizeof (uint32_t); i++) - { - ub[i] = seed; - seed = lcg_parkmiller (seed); - } - return buflen; + size_t size = buflen < sizeof (uint64_t) ? buflen : sizeof (uint64_t); + memcpy (buf, &seed, size); + return size; #endif /* __MINGW64_VERSION_MAJOR */ } @@ -359,7 +344,13 @@ init_rand_state (xorshift1024star_state* rs, const bool locked) __gthread_mutex_lock (&random_lock); if (!master_init) { - getosrandom (master_state, sizeof (master_state)); + uint64_t os_seed; + getosrandom (&os_seed, sizeof (os_seed)); + for (uint64_t i = 0; i < sizeof (master_state) / sizeof (uint64_t); i++) + { + os_seed = splitmix64 (os_seed); + master_state[i] = os_seed; + } njumps = 0; master_init = true; } |