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Justine Tunney 2020-06-15 07:18:57 -07:00
commit c91b3c5006
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libc/rand/rand64.c Normal file
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/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=8 sts=2 sw=2 fenc=utf-8 :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney │
│ │
│ This program is free software; you can redistribute it and/or modify │
│ it under the terms of the GNU General Public License as published by │
│ the Free Software Foundation; version 2 of the License. │
│ │
│ This program is distributed in the hope that it will be useful, but │
│ WITHOUT ANY WARRANTY; without even the implied warranty of │
│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU │
│ General Public License for more details. │
│ │
│ You should have received a copy of the GNU General Public License │
│ along with this program; if not, write to the Free Software │
│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
│ 02110-1301 USA │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/dce.h"
#include "libc/nexgen32e/x86feature.h"
#include "libc/rand/rand.h"
#include "libc/rand/xorshift.h"
/**
* Returns nondeterministic random number.
*
* This function uses a good random source if it's available, which
* takes ~400 cycles (~99ns). Otherwise it's seeded at program start
* with the system provided random value and may perform a few
* microseconds worth of system calls to get a good value.
*
* @see rngset()
*/
nodebuginfo uint64_t(rand64)(void) {
uint64_t res;
if (X86_HAVE(RDRND)) {
res = rdrand();
} else {
if (IsWindows()) {
res = winrandish();
} else {
devrand(&res, sizeof(res));
}
hidden extern uint64_t g_rando64;
res ^= MarsagliaXorshift64(&g_rando64);
}
return res;
}