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Justine Tunney 2020-06-15 07:18:57 -07:00
commit c91b3c5006
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libc/nexgen32e/doc/memrchr.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=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/dce.h"
#include "libc/str/str.h"
#define N 32
typedef uint8_t uint8_v _Vector_size(N);
/**
* Searches for last instance of character in memory region.
*
* @param s is binary data to search
* @param c is treated as unsigned char
* @param n is byte length of s
* @return address of last c in s, or NULL if not found
*/
void *memrchr(const void *s, int c, size_t n) {
unsigned char ch = (unsigned char)c;
const unsigned char *p = (const unsigned char *)s;
if (n >= 32 && CheckAvx2()) {
uint8_v cv;
__builtin_memset(&cv, ch, sizeof(cv));
do {
uint32_t skip;
uint8_v sv, tv;
memcpy(&sv, s + n - N, N);
asm("vpcmpeqb\t%2,%3,%1\n\t"
"vpmovmskb\t%1,%0\n\t"
"lzcnt\t%0,%0"
: "=r"(skip), "=x"(tv)
: "x"(sv), "x"(cv));
n -= skip;
if (skip != 32) break;
} while (n >= 32);
}
while (n--) {
if (p[n] == ch) return (/* unconst */ void *)&p[n];
}
return NULL;
}