48 lines
2.6 KiB
C
48 lines
2.6 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=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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│ This program 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; version 2 of the License. │
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│ │
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│ This program is distributed in the hope that it will be useful, but │
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│ WITHOUT ANY WARRANTY; without even the implied warranty of │
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│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU │
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│ 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 this program; if not, write to the Free Software │
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│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
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│ 02110-1301 USA │
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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/calls/calls.h"
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#include "libc/nexgen32e/x86feature.h"
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#include "libc/rand/rand.h"
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/**
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* Intel Secure Key Digital Random Number Generator
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* Introduced w/ Ivy Bridge c. 2013 and Excavator c. 2015
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* @see rand32(), rand64(), and randcpy()
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*/
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uint64_t rdrand(void) {
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char cf;
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size_t i;
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uint64_t res;
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assert(X86_HAVE(RDRND));
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for (;;) {
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for (i = 0; i < 10; ++i) {
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/* CF=1: Destination register valid. Quoth Intel DRNG-SIG 4.1.3 */
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asm volatile(CFLAG_ASM("rdrand\t%1")
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: CFLAG_CONSTRAINT(cf), "=r"(res)
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: /* no inputs */
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: "cc");
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if (cf) return res;
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}
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asm volatile("rep nop"); /* unlikely 140 cycle spin */
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}
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}
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