test_rng.h

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#pragma once
 
#include <core/intrinsics.h>
 
#include <memory.h>
#include <stdint.h>
 
typedef __uint128_t test_rng_state;
 
#define LCG_MULTIPLIER \
        ((((__uint128_t)0x0fc94e3bf4e9ab32ULL) << 64) + 0x866458cd56f5e605ULL)
 
#define lcg_init(rng_state, initseq) (rng_state) = ((initseq) << 1u) | 1u
 
#define lcg_random_u(rng_state)                                         \
__extension__({                                                         \
        (rng_state) *= LCG_MULTIPLIER;                                  \
        uint64_t __rng_val = (uint64_t)((rng_state) >> 64);             \
        __rng_val;                                                      \
})
 
#define lcg_random(rng_state)                                           \
__extension__({                                                         \
        uint64_t __u_val = lcg_random_u(rng_state);                     \
        double __ret = 0.0;                                             \
        if (__builtin_expect(!!__u_val, 1)) {                           \
                unsigned __lzs = intrinsics_clz(__u_val) + 1;           \
                __u_val <<= __lzs;                                      \
                __u_val >>= 12;                                         \
                                                                        \
                uint64_t __exp = 1023 - __lzs;                          \
                __u_val |= __exp << 52;                                 \
                                                                        \
                memcpy(&__ret, &__u_val, sizeof(double));               \
        }                                                               \
        __ret;                                                          \
})