/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-â
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â Copyright 2022 Justine Alexandra Roberts Tunney                              â
â                                                                              â
â Permission to use, copy, modify, and/or distribute this software for         â
â any purpose with or without fee is hereby granted, provided that the         â
â above copyright notice and this permission notice appear in all copies.      â
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â WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             â
â AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         â
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â PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               â
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â PERFORMANCE OF THIS SOFTWARE.                                                â
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#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;
}
