frillrun/include/jsw_rand.c

73 lines
1.3 KiB
C
Raw Normal View History

#include <limits.h>
#include <time.h>
#include "jsw_rand.h"
#define N 624
#define M 397
#define A 0x9908b0dfUL
#define U 0x80000000UL
#define L 0x7fffffffUL
/* Internal state */
static unsigned long x[N];
static int next;
/* Initialize internal state */
void jsw_seed ( unsigned long s )
{
int i;
x[0] = s & 0xffffffffUL;
for ( i = 1; i < N; i++ ) {
x[i] = ( 1812433253UL
* ( x[i - 1] ^ ( x[i - 1] >> 30 ) ) + i );
x[i] &= 0xffffffffUL;
}
}
/* Mersenne Twister */
unsigned long jsw_rand ( void )
{
unsigned long y, a;
int i;
/* Refill x if exhausted */
if ( next == N ) {
next = 0;
for ( i = 0; i < N - 1; i++ ) {
y = ( x[i] & U ) | x[i + 1] & L;
a = ( y & 0x1UL ) ? A : 0x0UL;
x[i] = x[( i + M ) % N] ^ ( y >> 1 ) ^ a;
}
y = ( x[N - 1] & U ) | x[0] & L;
a = ( y & 0x1UL ) ? A : 0x0UL;
x[N - 1] = x[M - 1] ^ ( y >> 1 ) ^ a;
}
y = x[next++];
/* Improve distribution */
y ^= (y >> 11);
y ^= (y << 7) & 0x9d2c5680UL;
y ^= (y << 15) & 0xefc60000UL;
y ^= (y >> 18);
return y;
}
/* Portable time seed */
unsigned jsw_time_seed()
{
time_t now = time ( 0 );
unsigned char *p = (unsigned char *)&now;
unsigned seed = 0;
size_t i;
for ( i = 0; i < sizeof now; i++ )
seed = seed * ( UCHAR_MAX + 2U ) + p[i];
return seed;
}