src/system/libroot/posix/string/strlen.cpp

   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 strlen(const char* string)
  18 {
  19         size_t length = 0;
  20
  21         /* Align access for four byte reads */
  22         for (; (((addr_t)string + length) & 3) != 0; length++) {
  23                 if (string[length] == '\0')
  24                         return length;
  25         }
  26
  27         /* Check four bytes for zero char */
  28         uint32* valuePointer = (uint32*)(string + length);
  29         for (; LACKS_ZERO_BYTE(*valuePointer); valuePointer++)
  30                 ;
  31
  32         /* Find the exact length */
  33         for (length = ((char*)valuePointer) - string; string[length] != '\0';
  34                 length++)
  35                 ;
  36
  37         return length;
  38 }