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2a8867a17f
New algorithm read the first aligned address and mask off the unwanted bytes (this strategy is similar to arch-specific implementations used on powerpc, sparc, and sh). The loop now read word-aligned address and check using the has_eq macro. Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc-linux-gnu, and powerpc64-linux-gnu by removing the arch-specific assembly implementation and disabling multi-arch (it covers both LE and BE for 64 and 32 bits). Co-authored-by: Richard Henderson <richard.henderson@linaro.org> Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>
89 lines
2.6 KiB
C
89 lines
2.6 KiB
C
/* Scan memory for a character. Generic version
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Copyright (C) 1991-2023 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but 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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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <libc-pointer-arith.h>
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#include <string-fzb.h>
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#include <string-fzc.h>
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#include <string-fzi.h>
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#include <string-shift.h>
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#include <string.h>
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#undef memchr
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#ifdef MEMCHR
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# define __memchr MEMCHR
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#endif
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static __always_inline const char *
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sadd (uintptr_t x, uintptr_t y)
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{
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return (const char *)(y > UINTPTR_MAX - x ? UINTPTR_MAX : x + y);
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}
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/* Search no more than N bytes of S for C. */
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void *
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__memchr (void const *s, int c_in, size_t n)
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{
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if (__glibc_unlikely (n == 0))
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return NULL;
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/* Read the first word, but munge it so that bytes before the array
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will not match goal. */
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const op_t *word_ptr = PTR_ALIGN_DOWN (s, sizeof (op_t));
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uintptr_t s_int = (uintptr_t) s;
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op_t word = *word_ptr;
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op_t repeated_c = repeat_bytes (c_in);
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/* Compute the address of the last byte taking in consideration possible
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overflow. */
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const char *lbyte = sadd (s_int, n - 1);
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/* And also the address of the word containing the last byte. */
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const op_t *lword = (const op_t *) PTR_ALIGN_DOWN (lbyte, sizeof (op_t));
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find_t mask = shift_find (find_eq_all (word, repeated_c), s_int);
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if (mask != 0)
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{
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char *ret = (char *) s + index_first (mask);
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return (ret <= lbyte) ? ret : NULL;
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}
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if (word_ptr == lword)
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return NULL;
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word = *++word_ptr;
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while (word_ptr != lword)
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{
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if (has_eq (word, repeated_c))
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return (char *) word_ptr + index_first_eq (word, repeated_c);
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word = *++word_ptr;
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}
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if (has_eq (word, repeated_c))
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{
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/* We found a match, but it might be in a byte past the end of the
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array. */
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char *ret = (char *) word_ptr + index_first_eq (word, repeated_c);
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if (ret <= lbyte)
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return ret;
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}
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return NULL;
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}
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#ifndef MEMCHR
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weak_alias (__memchr, memchr)
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libc_hidden_builtin_def (memchr)
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#endif
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