Function random_bounded_uint64

numpy/random/src/distributions/distributions.c:1391–1422

* Returns a single random npy_uint64 between off and off + rng * inclusive. The numbers wrap if rng is sufficiently large. */

 * inclusive. The numbers wrap if rng is sufficiently large.
 */
uint64_t random_bounded_uint64(bitgen_t *bitgen_state, uint64_t off,
                               uint64_t rng, uint64_t mask, bool use_masked) {
  if (rng == 0) {
    return off;
  } else if (rng <= 0xFFFFFFFFUL) {
    /* Call 32-bit generator if range in 32-bit. */
    if (rng == 0xFFFFFFFFUL) {
      /*
       * The 32-bit Lemire method does not handle rng=0xFFFFFFFF, so we'll
       * call next_uint32 directly.  This also works when use_masked is True,
       * so we handle both cases here.
       */
      return off + (uint64_t) next_uint32(bitgen_state);
    }
    if (use_masked) {
      return off + buffered_bounded_masked_uint32(bitgen_state, rng, mask, NULL,
                                                  NULL);
    } else {
      return off +
             buffered_bounded_lemire_uint32(bitgen_state, rng, NULL, NULL);
    }
  } else if (rng == 0xFFFFFFFFFFFFFFFFULL) {
    /* Lemire64 doesn't support inclusive rng = 0xFFFFFFFFFFFFFFFF. */
    return off + next_uint64(bitgen_state);
  } else {
    if (use_masked) {
      return off + bounded_masked_uint64(bitgen_state, rng, mask);
    } else {
      return off + bounded_lemire_uint64(bitgen_state, rng);
    }
  }
}

/*
 * Returns a single random npy_uint64 between off and off + rng