diff options
Diffstat (limited to 'src/common/mt_rand.c')
| -rw-r--r-- | src/common/mt_rand.c | 86 |
1 files changed, 42 insertions, 44 deletions
diff --git a/src/common/mt_rand.c b/src/common/mt_rand.c index 627d9dd..e4e8d12 100644 --- a/src/common/mt_rand.c +++ b/src/common/mt_rand.c @@ -48,71 +48,69 @@ #include <time.h> #include "mt_rand.h" -#define N (624) /* length of state vector */ -#define M (397) /* a period parameter */ -#define K (0x9908B0DFU) /* a magic constant */ -#define hiBit(u) ((u) & 0x80000000U) /* mask all but highest bit of u */ -#define loBit(u) ((u) & 0x00000001U) /* mask all but lowest bit of u */ -#define loBits(u) ((u) & 0x7FFFFFFFU) /* mask the highest bit of u */ -#define mixBits(u, v) (hiBit(u)|loBits(v)) /* move hi bit of u to hi bit of v */ +#define N 624 // length of state vector +#define M 397 // a period parameter +#define K 0x9908B0DFU // a magic constant -static unsigned long state[N + 1]; /* state vector + 1 extra to not violate ANSI C */ -static unsigned long *next; /* next random value is computed from here */ -static int left = -1; /* can *next++ this many times before reloading */ +#define hiBit(u) ((u) & 0x80000000U) // mask all but highest bit of u +#define loBit(u) ((u) & 0x00000001U) // mask all but lowest bit of u +#define loBits(u) ((u) & 0x7FFFFFFFU) // mask the highest bit of u +#define mixBits(u, v) (hiBit(u)|loBits(v)) // move hi bit of u to hi bit of v -void mt_seed (unsigned long seed) +static uint32_t state[N+1]; // state vector the +1 is needed due to the coding +static uint32_t *next; // next random value is computed from here +static int left = -1; // can *next++ this many times before reloading + +void mt_seed (uint32_t seed) { - register unsigned long x = (seed | 1U) & 0xFFFFFFFFU, *s = state; - register int j; + uint32_t x = seed | 1U; + uint32_t *s = state; + left = 0; - for (left = 0, *s++ = x, j = N; --j; *s++ = (x *= 69069U) & 0xFFFFFFFFU); + for (int j = N; *s++ = x, --j; x *= 69069U); } -unsigned long mt_reload (void) +void mt_reload (void) { - register unsigned long *p0 = state, *p2 = state + 2, *pM = - state + M, s0, s1; - register int j; - + // if mt_seed has never been called if (left < -1) mt_seed (time (NULL)); - left = N - 1, next = state + 1; + // conceptually, these are indices into the state that wrap + uint32_t *p0 = state; + uint32_t *p2 = state + 2; + uint32_t *pM = state + M; + + uint32_t s0 = state[0]; + uint32_t s1 = state[1]; - for (s0 = state[0], s1 = state[1], j = N - M + 1; --j; - s0 = s1, s1 = *p2++) + // regenerate the lower N-M elements of the state + for (int j = N-M+1; --j != 0; s0 = s1, s1 = *p2++) *p0++ = *pM++ ^ (mixBits (s0, s1) >> 1) ^ (loBit (s1) ? K : 0U); - for (pM = state, j = M; --j; s0 = s1, s1 = *p2++) + pM = state; + // regenerate the next M-1 elements of the state + // note that s1 is set to state[N] at the end, but discarded + for (int j = M; --j != 0; s0 = s1, s1 = *p2++) *p0++ = *pM++ ^ (mixBits (s0, s1) >> 1) ^ (loBit (s1) ? K : 0U); - s1 = state[0], *p0 = - *pM ^ (mixBits (s0, s1) >> 1) ^ (loBit (s1) ? K : 0U); - s1 ^= (s1 >> 11); - s1 ^= (s1 << 7) & 0x9D2C5680U; - s1 ^= (s1 << 15) & 0xEFC60000U; - return (s1 ^ (s1 >> 18)); + // regenerate the last 1 element of the state + s1 = state[0]; + *p0 = *pM ^ (mixBits (s0, s1) >> 1) ^ (loBit (s1) ? K : 0U); + + // ready for the normal mt_random algorithm + left = N; + next = state; } -unsigned long mt_random (void) +uint32_t mt_random (void) { - unsigned long y; - if (--left < 0) - return (mt_reload ()); + mt_reload (); - y = *next++; + uint32_t y = *next++; y ^= (y >> 11); y ^= (y << 7) & 0x9D2C5680U; y ^= (y << 15) & 0xEFC60000U; - return (y ^ (y >> 18)); -} - -int mt_rand (void) -{ - unsigned long r = mt_random (); - while (r >> 16) - r = (r & 0xFFFF) + (r >> 16); - - return (r); + return y ^ (y >> 18); } |