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