/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8                               :vi │
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
│                                                                              │
│ Permission to use, copy, modify, and/or distribute this software for         │
│ any purpose with or without fee is hereby granted, provided that the         │
│ above copyright notice and this permission notice appear in all copies.      │
│                                                                              │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
│ PERFORMANCE OF THIS SOFTWARE.                                                │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/stdio/rand.h"

/**
 * Returns linear congruential deterministic pseudorandom data, e.g.
 *
 *     uint64_t x = lemur64();
 *
 * You can generate different types of numbers as follows:
 *
 *     int64_t x = lemur64() >> 1;    // make positive signed integer
 *     double x = _real1(lemur64());  // make float on [0,1]-interval
 *
 * If you want a fast pseudorandom number generator that seeds itself
 * automatically on startup and fork(), then consider _rand64. If you
 * want true random data then consider rdseed, rdrand, and getrandom.
 *
 * @return 64 bits of pseudorandom data
 * @note this is Lemire's Lehmer generator
 * @note this function takes at minimum 1 cycle
 * @note this function passes bigcrush and practrand
 * @note this function is not intended for cryptography
 * @see _rand64(), rngset(), _real1(), _real2(), _real3()
 */
uint64_t lemur64(void) {
  static uint128_t s = 2131259787901769494;
  return (s *= 15750249268501108917ull) >> 64;
}
