mirror of
https://git.sr.ht/~cismonx/bookmarkfs
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97 lines
2.3 KiB
C
97 lines
2.3 KiB
C
/**
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* bookmarkfs/src/prng.c
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*
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* Non-cryptographic pseudo-random number generator.
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* ----
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*
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* Copyright (C) 2024 CismonX <admin@cismon.net>
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*
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* This file is part of BookmarkFS.
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*
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* BookmarkFS is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* BookmarkFS is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with BookmarkFS. If not, see <https://www.gnu.org/licenses/>.
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*/
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#ifdef HAVE_CONFIG_H
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# include "config.h"
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#endif
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#include "prng.h"
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#include <errno.h>
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#include <inttypes.h>
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#include <string.h>
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#include <sys/random.h>
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#include "xstd.h"
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// Forward declaration start
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static uint64_t rotl64 (uint64_t, unsigned);
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// Forward declaration end
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static uint64_t state[4];
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static uint64_t
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rotl64 (
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uint64_t val,
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unsigned n
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) {
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return (val << n) | (val >> (64 - n));
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}
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/**
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* The xoshiro256++ PRNG.
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*
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* See: <https://prng.di.unimi.it/xoshiro256plusplus.c>
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*/
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uint64_t
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prng_rand (void)
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{
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uint64_t result = rotl64(state[0] + state[3], 23) + state[0];
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uint64_t tmp = state[1] << 17;
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state[2] ^= state[0];
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state[3] ^= state[1];
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state[1] ^= state[2];
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state[0] ^= state[3];
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state[2] ^= tmp;
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state[3] = rotl64(state[3], 45);
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return result;
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}
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int
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prng_seed (
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uint64_t const s[4]
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) {
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if (s != NULL) {
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memcpy(state, s, sizeof(state));
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return 0;
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}
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ssize_t nbytes = getrandom(state, sizeof(state), 0);
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if (unlikely(nbytes < 0)) {
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log_printf("getrandom(): %s", xstrerror(errno));
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return -1;
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}
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// For reads up to 256 bytes, getrandom() always returns
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// as many bytes as requested.
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// This is guaranteed on both Linux and FreeBSD.
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debug_assert(nbytes == sizeof(state));
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debug_printf("prng seed: "
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"%016" PRIx64 "%016" PRIx64 "%016" PRIx64 "%016" PRIx64,
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state[0], state[1], state[2], state[3]);
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return 0;
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}
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