xorshiftrng128.c

#include <stdint.h>
uint64_t s[2];

uint64_t 
xorshiftrng128(void) 
{
  uint64_t s1 = s[0];
  uint64_t s0 = s[1];
  uint64_t result = s0 + s1;
  
  s[0] = s0;
  s1 ^= s1 << 23; // a
  s[1] = s1 ^ s0 ^ (s1 >> 18) ^ (s0 >> 5); // b, c
  
  return result;
}