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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=2 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/assert.h"
#include "libc/bits/bits.h"
#include "libc/calls/calls.h"
#include "libc/nexgen32e/x86feature.h"
#include "libc/rand/rand.h"
/**
* Intel Secure Key Digital Random Number Generator
* Introduced w/ Ivy Bridge c. 2013 and Excavator c. 2015
* @see rand32(), rand64(), and randcpy()
*/
uint64_t rdrand(void) {
char cf;
size_t i;
uint64_t res;
assert(X86_HAVE(RDRND));
for (;;) {
for (i = 0; i < 10; ++i) {
/* CF=1: Destination register valid. Quoth Intel DRNG-SIG 4.1.3 */
asm volatile(CFLAG_ASM("rdrand\t%1")
: CFLAG_CONSTRAINT(cf), "=r"(res)
: /* no inputs */
: "cc");
if (cf) return res;
}
asm volatile("rep nop"); /* unlikely 140 cycle spin */
}
}