1/* 2 * Copyright 2010 Tilera Corporation. All Rights Reserved. 3 * 4 * This program is free software; you can redistribute it and/or 5 * modify it under the terms of the GNU General Public License 6 * as published by the Free Software Foundation, version 2. 7 * 8 * This program is distributed in the hope that it will be useful, but 9 * WITHOUT ANY WARRANTY; without even the implied warranty of 10 * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or 11 * NON INFRINGEMENT. See the GNU General Public License for 12 * more details. 13 */ 14 15#include <linux/types.h> 16#include <linux/string.h> 17#include <linux/module.h> 18 19void *memchr(const void *s, int c, size_t n) 20{ 21 /* Get an aligned pointer. */ 22 const uintptr_t s_int = (uintptr_t) s; 23 const uint32_t *p = (const uint32_t *)(s_int & -4); 24 25 /* Create four copies of the byte for which we are looking. */ 26 const uint32_t goal = 0x01010101 * (uint8_t) c; 27 28 /* Read the first word, but munge it so that bytes before the array 29 * will not match goal. 30 * 31 * Note that this shift count expression works because we know 32 * shift counts are taken mod 32. 33 */ 34 const uint32_t before_mask = (1 << (s_int << 3)) - 1; 35 uint32_t v = (*p | before_mask) ^ (goal & before_mask); 36 37 /* Compute the address of the last byte. */ 38 const char *const last_byte_ptr = (const char *)s + n - 1; 39 40 /* Compute the address of the word containing the last byte. */ 41 const uint32_t *const last_word_ptr = 42 (const uint32_t *)((uintptr_t) last_byte_ptr & -4); 43 44 uint32_t bits; 45 char *ret; 46 47 if (__builtin_expect(n == 0, 0)) { 48 /* Don't dereference any memory if the array is empty. */ 49 return NULL; 50 } 51 52 while ((bits = __insn_seqb(v, goal)) == 0) { 53 if (__builtin_expect(p == last_word_ptr, 0)) { 54 /* We already read the last word in the array, 55 * so give up. 56 */ 57 return NULL; 58 } 59 v = *++p; 60 } 61 62 /* We found a match, but it might be in a byte past the end 63 * of the array. 64 */ 65 ret = ((char *)p) + (__insn_ctz(bits) >> 3); 66 return (ret <= last_byte_ptr) ? ret : NULL; 67} 68EXPORT_SYMBOL(memchr); 69