3edabee2ed
This change fixes a bug that memchr() will read the first word of the source even if the length is zero. Ironically, the code was originally written with a test to avoid exactly this problem, but to make the code conform to Linux coding standards with all declarations preceding all statements, the first load from memory was moved up above that test as the initial value for a variable. The change just moves all the variable declarations to the top of the file, with no initializers, so that the test can also be at the top of the file. Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
71 lines
2 KiB
C
71 lines
2 KiB
C
/*
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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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const uint32_t *last_word_ptr;
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const uint32_t *p;
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const char *last_byte_ptr;
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uintptr_t s_int;
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uint32_t goal, before_mask, v, 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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/* Get an aligned pointer. */
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s_int = (uintptr_t) s;
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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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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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before_mask = (1 << (s_int << 3)) - 1;
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v = (*p | before_mask) ^ (goal & before_mask);
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/* Compute the address of the last byte. */
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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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last_word_ptr = (const uint32_t *)((uintptr_t) last_byte_ptr & -4);
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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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