PRNG with seeding and output - see link in code

Collatz-Weyl.c

// https://www.reddit.com/r/RNG/comments/19a2q24/collatzweyl_generators/?utm_source=share&utm_medium=web2x&context=3

// $ gcc -Wall -O3 Collatz-Weyl.c -o Collatz-Weyl
// $ ./Collatz-Weyl | pv > /dev/null <-- 650MiB/s on 2018 Zeon VM
//                         compared with 400MiB/s for ChaCha20

#include <stdio.h>
#include <assert.h>

static __uint128_t c[4] = {0, 0, 0, 0}; // c[0] must be odd

__uint128_t CWG128(void) {
  c[1] = (c[1] >> 1) * ((c[2] += c[1]) | 1) ^ (c[3] += c[0]);
  return c[2] >> 96 ^ c[1];
}

int main(void) {
  FILE * fr = fopen("/dev/random", "r");
  assert(fr);
  assert(1 == fread(&c[0], sizeof(c[0]), 1, fr));
  fclose(fr);
  c[0] |= 1U; // odd
  for(int i=0; i<96; i++) CWG128();
  while(1) {
    __uint128_t o = CWG128();
    fwrite(&o, sizeof(o), 1, stdout);
  }
  return(0);
}