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 19#undef strchr 20 21char *strchr(const char *s, int c) 22{ 23 int z, g; 24 25 /* Get an aligned pointer. */ 26 const uintptr_t s_int = (uintptr_t) s; 27 const uint32_t *p = (const uint32_t *)(s_int & -4); 28 29 /* Create four copies of the byte for which we are looking. */ 30 const uint32_t goal = 0x01010101 * (uint8_t) c; 31 32 /* Read the first aligned word, but force bytes before the string to 33 * match neither zero nor goal (we make sure the high bit of each 34 * byte is 1, and the low 7 bits are all the opposite of the goal 35 * byte). 36 * 37 * Note that this shift count expression works because we know shift 38 * counts are taken mod 32. 39 */ 40 const uint32_t before_mask = (1 << (s_int << 3)) - 1; 41 uint32_t v = (*p | before_mask) ^ (goal & __insn_shrib(before_mask, 1)); 42 43 uint32_t zero_matches, goal_matches; 44 while (1) { 45 /* Look for a terminating '\0'. */ 46 zero_matches = __insn_seqb(v, 0); 47 48 /* Look for the goal byte. */ 49 goal_matches = __insn_seqb(v, goal); 50 51 if (__builtin_expect(zero_matches | goal_matches, 0)) 52 break; 53 54 v = *++p; 55 } 56 57 z = __insn_ctz(zero_matches); 58 g = __insn_ctz(goal_matches); 59 60 /* If we found c before '\0' we got a match. Note that if c == '\0' 61 * then g == z, and we correctly return the address of the '\0' 62 * rather than NULL. 63 */ 64 return (g <= z) ? ((char *)p) + (g >> 3) : NULL; 65} 66EXPORT_SYMBOL(strchr); 67