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