newlib/libc/string/stpncpy.c

   1 /*
   2 FUNCTION
   3         <<stpncpy>>---counted copy string returning a pointer to its end
   4
   5 INDEX
   6         stpncpy
   7
   8 SYNOPSIS
   9         #include <string.h>
  10         char *stpncpy(char *restrict <[dst]>, const char *restrict <[src]>,
  11                       size_t <[length]>);
  12
  13 DESCRIPTION
  14         <<stpncpy>> copies not more than <[length]> characters from the
  15         the string pointed to by <[src]> (including the terminating
  16         null character) to the array pointed to by <[dst]>.  If the
  17         string pointed to by <[src]> is shorter than <[length]>
  18         characters, null characters are appended to the destination
  19         array until a total of <[length]> characters have been
  20         written.
  21
  22 RETURNS
  23         This function returns a pointer to the end of the destination string,
  24         thus pointing to the trailing '\0', or, if the destination string is
  25         not null-terminated, pointing to dst + n.
  26
  27 PORTABILITY
  28 <<stpncpy>> is a GNU extension, candidate for inclusion into POSIX/SUSv4.
  29
  30 <<stpncpy>> requires no supporting OS subroutines.
  31
  32 QUICKREF
  33         stpncpy gnu
  34 */
  35
  36 #include <string.h>
  37 #include <limits.h>
  38
  39 /*SUPPRESS 560*/
  40 /*SUPPRESS 530*/
  41
  42 /* Nonzero if either X or Y is not aligned on a "long" boundary.  */
  43 #define UNALIGNED(X, Y) \
  44   (((long)X & (sizeof (long) - 1)) | ((long)Y & (sizeof (long) - 1)))
  45
  46 #if LONG_MAX == 2147483647L
  47 #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
  48 #else
  49 #if LONG_MAX == 9223372036854775807L
  50 /* Nonzero if X (a long int) contains a NULL byte. */
  51 #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
  52 #else
  53 #error long int is not a 32bit or 64bit type.
  54 #endif
  55 #endif
  56
  57 #ifndef DETECTNULL
  58 #error long int is not a 32bit or 64bit byte
  59 #endif
  60
  61 #define TOO_SMALL(LEN) ((LEN) < sizeof (long))
  62
  63 char *
  64 stpncpy (char *__restrict dst,
  65         const char *__restrict src,
  66         size_t count)
  67 {
  68   char *ret = NULL;
  69
  70 #if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__)
  71   long *aligned_dst;
  72   const long *aligned_src;
  73
  74   /* If SRC and DEST is aligned and count large enough, then copy words.  */
  75   if (!UNALIGNED (src, dst) && !TOO_SMALL (count))
  76     {
  77       aligned_dst = (long*)dst;
  78       aligned_src = (long*)src;
  79
  80       /* SRC and DEST are both "long int" aligned, try to do "long int"
  81          sized copies.  */
  82       while (count >= sizeof (long int) && !DETECTNULL(*aligned_src))
  83         {
  84           count -= sizeof (long int);
  85           *aligned_dst++ = *aligned_src++;
  86         }
  87
  88       dst = (char*)aligned_dst;
  89       src = (char*)aligned_src;
  90     }
  91 #endif /* not PREFER_SIZE_OVER_SPEED */
  92
  93   while (count > 0)
  94     {
  95       --count;
  96       if ((*dst++ = *src++) == '\0')
  97         {
  98           ret = dst - 1;
  99           break;
 100         }
 101     }
 102
 103   while (count-- > 0)
 104     *dst++ = '\0';
 105
 106   return ret ? ret : dst;
 107 }