1 /* 2 * Copyright 2013 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 strnlen(const char * s,size_t count)19size_t strnlen(const char *s, size_t count) 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 size_t bytes_read = sizeof(*p) - (s_int & (sizeof(*p) - 1)); 25 size_t len; 26 uint32_t v, bits; 27 28 /* Avoid page fault risk by not reading any bytes when count is 0. */ 29 if (count == 0) 30 return 0; 31 32 /* Read first word, but force bytes before the string to be nonzero. */ 33 v = *p | ((1 << ((s_int << 3) & 31)) - 1); 34 35 while ((bits = __insn_seqb(v, 0)) == 0) { 36 if (bytes_read >= count) { 37 /* Read COUNT bytes and didn't find the terminator. */ 38 return count; 39 } 40 v = *++p; 41 bytes_read += sizeof(v); 42 } 43 44 len = ((const char *) p) + (__insn_ctz(bits) >> 3) - s; 45 return (len < count ? len : count); 46 } 47 EXPORT_SYMBOL(strnlen); 48