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46 lines
2.7 KiB
C
46 lines
2.7 KiB
C
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/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2022 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/rand/rand.h"
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/**
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* Returns linear congruential deterministic pseudorandom data, e.g.
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*
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* uint64_t x = lemur64();
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*
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* You can generate different types of numbers as follows:
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*
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* int64_t x = lemur64() >> 1; // make positive signed integer
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* double x = _real1(lemur64()); // make float on [0,1]-interval
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*
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* If you want a fast pseudorandom number generator that seeds itself
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* automatically on startup and fork() then consider rand64(). If you
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* want true random data then consider rdseed, rdrand, and getrandom.
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*
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* @return 64 bits of pseudorandom data
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* @note this is Lemire's Lehmer generator
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* @note this function takes at minimum 1 cycle
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* @note this function passes bigcrush and practrand
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* @note this function is not intended for cryptography
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* @see rand64(), rngset(), _real1(), _real2(), _real3()
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*/
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uint64_t lemur64(void) {
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static uint128_t s = 2131259787901769494;
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return (s *= 15750249268501108917ull) >> 64;
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}
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