ra8_rand_stub.c

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#include <stdint.h>
#include <stdlib.h>

typedef enum : uint32_t {
  k_xorshift_a = 13U, 
  k_xorshift_b = 17U, 
  k_xorshift_c = 5U,  
} xorshift32_param_t;

typedef enum : uint32_t {
  k_ra8_rand_default_seed = 0x9E3779B9UL, 
} ra8_rand_const_t;
 
static uint32_t s_state = (uint32_t)k_ra8_rand_default_seed;

void srand(unsigned int seed)
{
  /* Avoid the all-zero state which would lock xorshift. */
  s_state = (seed == 0U) ? (uint32_t)k_ra8_rand_default_seed : (uint32_t)seed;
}

int rand(void)
{
  /* Marsaglia xorshift32 with constants 13/17/5. */
  uint32_t       x      = s_state;
  const uint32_t k_mask = (uint32_t)RAND_MAX;
  x ^= x << k_xorshift_a;
  x ^= x >> k_xorshift_b;
  x ^= x << k_xorshift_c;
  s_state = x;
  return (int)(x & k_mask);
}