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67 lines
3 KiB
C
67 lines
3 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 2021 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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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/str/str.h"
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noasan static const char *strchr_x64(const char *p, uint64_t c) {
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unsigned a, b;
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uint64_t w, x, y;
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for (c *= 0x0101010101010101;; p += 8) {
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w = READ64LE(p);
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if ((x = ~(w ^ c) & ((w ^ c) - 0x0101010101010101) & 0x8080808080808080) |
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(y = ~w & (w - 0x0101010101010101) & 0x8080808080808080)) {
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if (x) {
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a = __builtin_ctzll(x);
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if (y) {
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b = __builtin_ctzll(y);
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if (a <= b) {
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return p + (a >> 3);
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} else {
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return NULL;
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}
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} else {
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return p + (a >> 3);
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}
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} else {
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return NULL;
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}
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}
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}
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}
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/**
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* Returns pointer to first instance of character.
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*
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* @param s is a NUL-terminated string
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* @param c is masked with 255 as byte to search for
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* @return pointer to first instance of c or NULL if not found
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* noting that if c is NUL we return pointer to terminator
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* @asyncsignalsafe
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*/
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char *strchr(const char *s, int c) {
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char *r;
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for (c &= 0xff; (uintptr_t)s & 7; ++s) {
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if ((*s & 0xff) == c) return s;
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if (!*s) return NULL;
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}
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r = strchr_x64(s, c);
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assert(!r || *r || !c);
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return r;
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}
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