mirror of
https://github.com/jart/cosmopolitan.git
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29bf8b1a30
- Make rand64() thread safe - Introduce lemur64 lcg prng - Improve strace on New Technology - Improve msync() on New Technology
95 lines
4.1 KiB
C
95 lines
4.1 KiB
C
/*-*- 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=8 sts=2 sw=2 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2020 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/assert.h"
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#include "libc/bits/bits.h"
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#include "libc/bits/lockcmpxchg16b.internal.h"
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#include "libc/bits/lockxadd.internal.h"
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#include "libc/bits/weaken.h"
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#include "libc/calls/calls.h"
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#include "libc/intrin/kprintf.h"
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#include "libc/nexgen32e/rdtsc.h"
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#include "libc/nt/thread.h"
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#include "libc/rand/rand.h"
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#include "libc/runtime/runtime.h"
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#include "libc/sysv/consts/auxv.h"
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#include "libc/thread/create.h"
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extern int __pid;
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static int thepid;
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static int thecount;
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static uint128_t thepool;
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/**
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* Returns nondeterministic random data.
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*
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* This function is similar to lemur64() except it'thepool intended to
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* be unpredictable. This PRNG automatically seeds itself on startup
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* using a much stronger and faster random source than `srand(time(0))`.
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* This function will automatically reseed itself when new processes and
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* threads are spawned. This function is thread safe in the sense that a
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* race condition can't happen where two threads return the same result.
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*
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* @see rdseed(), rdrand(), rand(), random(), rngset()
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* @note this function is not intended for cryptography
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* @note this function passes bigcrush and practrand
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* @note this function takes at minimum 30 cycles
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* @asyncsignalsafe
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* @threadsafe
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* @vforksafe
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*/
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uint64_t rand64(void) {
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void *d;
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int c1, p1, p2;
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uint128_t s1, s2;
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do {
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p1 = __pid;
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p2 = thepid;
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c1 = thecount;
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asm volatile("" ::: "memory");
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s1 = thepool;
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if (p1 == p2) {
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// fast path
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s2 = s1;
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} else {
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// slow path
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if (!p2) {
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// first call so get some cheap entropy
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if ((d = (void *)getauxval(AT_RANDOM))) {
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memcpy(&s2, d, 16); // kernel entropy
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} else {
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s2 = kStartTsc; // rdtsc() @ _start()
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}
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} else {
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// process contention so blend a timestamp
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s2 = s1 ^ rdtsc();
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}
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// toss the new pid in there
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s2 ^= p1;
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// ordering for thepid probably doesn't matter
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thepid = p1;
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}
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// lemur64 pseudorandom number generator
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s2 *= 15750249268501108917ull;
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// sadly 128-bit values aren't atomic on x86
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_lockcmpxchg16b(&thepool, &s1, s2);
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// do it again if there's thread contention
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} while (_lockxadd(&thecount, 1) != c1);
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// the most important step in the prng
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return s2 >> 64;
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}
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