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

   1 /*
   2 ** Copyright 2001, Travis Geiselbrecht. All rights reserved.
   3 ** Distributed under the terms of the NewOS License.
   4 */
   5
   6 #include <sys/types.h>
   7 #include <string.h>
   8 #include <SupportDefs.h>
   9
  10
  11 /* From Bit twiddling hacks:
  12         http://graphics.stanford.edu/~seander/bithacks.html */
  13 #define LACKS_ZERO_BYTE(value) \
  14         (((value - 0x01010101) & ~value & 0x80808080) == 0)
  15
  16
  17 char*
  18 strncpy(char* dest, const char* src, size_t count)
  19 {
  20         char* tmp = dest;
  21
  22         // Align destination buffer for four byte writes.
  23         while (((addr_t)dest & 3) != 0 && count != 0) {
  24                 count--;
  25                 if ((*dest++ = *src++) == '\0') {
  26                         memset(dest, '\0', count);
  27                         return tmp;
  28                 }
  29         }
  30
  31         if (count == 0)
  32                 return tmp;
  33
  34         if (((addr_t)src & 3) == 0) {
  35                 // If the source and destination are aligned, copy a word
  36                 // word at a time
  37                 uint32* alignedSrc = (uint32*)src;
  38                 uint32* alignedDest = (uint32*)dest;
  39                 size_t alignedCount = count / 4;
  40                 count -= alignedCount * 4;
  41
  42                 for (; alignedCount != 0 && LACKS_ZERO_BYTE(*alignedSrc);
  43                                 alignedCount--)
  44                         *alignedDest++ = *alignedSrc++;
  45
  46                 count += alignedCount * 4;
  47                 src = (char*)alignedSrc;
  48                 dest = (char*)alignedDest;
  49         }
  50
  51         // Deal with the remainder.
  52         while (count-- != 0) {
  53                 if ((*dest++ = *src++) == '\0') {
  54                         memset(dest, '\0', count);
  55                         return tmp;
  56                 }
  57         }
  58
  59         return tmp;
  60 }
  61