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/* “An experimental exploration of Marsaglia’s xorshift generators,
* scrambled”, Sebastiano Vigna */
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <assert.h>
#include <unistd.h>
#include "xorshift.h"
uint64_t xorshift_step (randctx * const st) {
uint64_t s0 = st->s[ st->p ];
uint64_t s1 = st->s[ st->p = ( st->p + 1 ) & (XORSHIFT_S-1) ];
s1 ^= s1 << 31; // a
s1 ^= s1 >> 11; // b
s0 ^= s0 >> 30; // c
return ( st->s[ st->p ] = s0 ^ s1 ) * 1181783497276652981LL;
}
static uint64_t rand64 () {
unsigned long long rand;
while (!__builtin_ia32_rdrand64_step (&rand));
return rand;
}
void xorshift_seed (randctx * const st) {
/* seed with high-quality randomness */
for (unsigned char i = 0; i < XORSHIFT_S; i++) {
st->s[i] = rand64 ();
}
}
#if 0
uint64_t xorshift_step (randctx * const st) {
uint64_t x = st->s[0];
x ^= x >> 12; // a
x ^= x << 25; // b
x ^= x >> 27; // c
st->s[0] = x;
return x * 2685821657736338717LL;
}
#endif
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