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71 lines
2.0 KiB
71 lines
2.0 KiB
/* |
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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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