forked from Minki/linux
69 lines
2.0 KiB
C
69 lines
2.0 KiB
C
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/*
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* Copyright 2010 Tilera Corporation. All Rights Reserved.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation, version 2.
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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, GOOD TITLE or
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* NON INFRINGEMENT. See the GNU General Public License for
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* more details.
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*/
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#include <linux/types.h>
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#include <linux/string.h>
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#include <linux/module.h>
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void *memchr(const void *s, int c, size_t n)
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{
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/* Get an aligned pointer. */
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const uintptr_t s_int = (uintptr_t) s;
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const uint32_t *p = (const uint32_t *)(s_int & -4);
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/* Create four copies of the byte for which we are looking. */
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const uint32_t goal = 0x01010101 * (uint8_t) c;
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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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*
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* Note that this shift count expression works because we know
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* shift counts are taken mod 32.
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*/
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const uint32_t before_mask = (1 << (s_int << 3)) - 1;
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uint32_t v = (*p | before_mask) ^ (goal & before_mask);
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/* Compute the address of the last byte. */
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const char *const last_byte_ptr = (const char *)s + n - 1;
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/* Compute the address of the word containing the last byte. */
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const uint32_t *const last_word_ptr =
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(const uint32_t *)((uintptr_t) last_byte_ptr & -4);
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uint32_t bits;
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char *ret;
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if (__builtin_expect(n == 0, 0)) {
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/* Don't dereference any memory if the array is empty. */
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return NULL;
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}
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while ((bits = __insn_seqb(v, goal)) == 0) {
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if (__builtin_expect(p == last_word_ptr, 0)) {
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/* We already read the last word in the array,
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* so give up.
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*/
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return NULL;
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}
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v = *++p;
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}
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/* We found a match, but it might be in a byte past the end
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* of the array.
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*/
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ret = ((char *)p) + (__insn_ctz(bits) >> 3);
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return (ret <= last_byte_ptr) ? ret : NULL;
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}
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EXPORT_SYMBOL(memchr);
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