mirror of
https://github.com/jart/cosmopolitan.git
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2ab9e9f7fd
- Introduce portable sched_getcpu() api - Support GCC's __target_clones__ feature - Make fma() go faster on x86 in default mode - Remove some asan checks from core libraries - WinMain() now ensures $HOME and $USER are defined
57 lines
3 KiB
C
57 lines
3 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│ vi: set et ft=c ts=2 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/intrin/asmflag.h"
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#include "libc/nexgen32e/x86feature.h"
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#include "libc/stdio/rand.h"
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#include "libc/stdio/stdio.h"
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#include "libc/sysv/consts/grnd.h"
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/**
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* Retrieves 64-bits of true random data from RDSEED instruction.
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*
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* If RDSEED isn't available, we'll try RDRAND (which we automatically
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* disable for microarchitectures where it's known to be slow or buggy).
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* If RDRAND isn't available then we try getrandom(), ProcessPrng(), or
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* sysctl(KERN_ARND). If those aren't available then we try /dev/urandom
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* and if that fails, we use RDTSC and getpid().
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*
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* @note this function could block a nontrivial time on old computers
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* @note this function is indeed intended for cryptography
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* @note this function takes around 800 cycles
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* @see rngset(), rdrand(), _rand64()
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* @asyncsignalsafe
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* @vforksafe
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*/
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uint64_t rdseed(void) {
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int i;
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char cf;
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uint64_t x;
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if (X86_HAVE(RDSEED)) {
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for (i = 0; i < 10; ++i) {
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asm volatile(CFLAG_ASM("rdseed\t%1")
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: CFLAG_CONSTRAINT(cf), "=r"(x)
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: /* no inputs */
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: "cc");
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if (cf) return x;
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asm volatile("pause");
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}
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}
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return rdrand();
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}
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