1 /* 2 ** Copyright 2001, Travis Geiselbrecht. All rights reserved. 3 ** Distributed under the terms of the NewOS License. 4 */ 5 6 #include <string.h> 7 #include <SupportDefs.h> 8 9 10 /* From Bit twiddling hacks: 11 http://graphics.stanford.edu/~seander/bithacks.html */ 12 #define LACKS_ZERO_BYTE(value) \ 13 (((value - 0x01010101) & ~value & 0x80808080) == 0) 14 15 16 size_t 17 strnlen(const char* string, size_t count) 18 { 19 size_t length = 0; 20 /* Align access for four byte reads */ 21 for (; (((addr_t)string + length) & 3) != 0; length++) { 22 if (length == count || string[length] == '\0') 23 return length; 24 } 25 26 /* Check four bytes for zero char */ 27 const uint32* kMaxScanPosition = (uint32*)(string + count - 4); 28 uint32* valuePointer = (uint32*)(string + length); 29 for (; valuePointer <= kMaxScanPosition && LACKS_ZERO_BYTE(*valuePointer); 30 valuePointer++) 31 ; 32 33 /* Find the exact length */ 34 for (length = ((char*)valuePointer) - string; length < count 35 && string[length] != '\0'; length++) 36 ; 37 38 return length; 39 } 40