toolchain/gcc/newlib/libc/string/strncpy.c

   1 /*
   2 FUNCTION
   3         <<strncpy>>---counted copy string
   4
   5 INDEX
   6         strncpy
   7
   8 ANSI_SYNOPSIS
   9         #include <string.h>
  10         char *strncpy(char *<[dst]>, const char *<[src]>, size_t <[length]>);
  11
  12 TRAD_SYNOPSIS
  13         #include <string.h>
  14         char *strncpy(<[dst]>, <[src]>, <[length]>)
  15         char *<[dst]>;
  16         char *<[src]>;
  17         size_t <[length]>;
  18
  19 DESCRIPTION
  20         <<strncpy>> copies not more than <[length]> characters from the
  21         the string pointed to by <[src]> (including the terminating
  22         null character) to the array pointed to by <[dst]>.  If the
  23         string pointed to by <[src]> is shorter than <[length]>
  24         characters, null characters are appended to the destination
  25         array until a total of <[length]> characters have been
  26         written.
  27
  28 RETURNS
  29         This function returns the initial value of <[dst]>.
  30
  31 PORTABILITY
  32 <<strncpy>> is ANSI C.
  33
  34 <<strncpy>> requires no supporting OS subroutines.
  35
  36 QUICKREF
  37         strncpy ansi pure
  38 */
  39
  40 #include <string.h>
  41 #include <limits.h>
  42
  43 /*SUPPRESS 560*/
  44 /*SUPPRESS 530*/
  45
  46 /* Nonzero if either X or Y is not aligned on a "long" boundary.  */
  47 #define UNALIGNED(X, Y) \
  48   (((long)X & (sizeof (long) - 1)) | ((long)Y & (sizeof (long) - 1)))
  49
  50 #if LONG_MAX == 2147483647L
  51 #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
  52 #else
  53 #if LONG_MAX == 9223372036854775807L
  54 /* Nonzero if X (a long int) contains a NULL byte. */
  55 #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
  56 #else
  57 #error long int is not a 32bit or 64bit type.
  58 #endif
  59 #endif
  60
  61 #ifndef DETECTNULL
  62 #error long int is not a 32bit or 64bit byte
  63 #endif
  64
  65 #define TOO_SMALL(LEN) ((LEN) < sizeof (long))
  66
  67 char *
  68 _DEFUN (strncpy, (dst0, src0),
  69         char *dst0 _AND
  70         _CONST char *src0 _AND
  71         size_t count)
  72 {
  73 #if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
  74   char *dscan;
  75   _CONST char *sscan;
  76
  77   dscan = dst0;
  78   sscan = src0;
  79   while (count > 0)
  80     {
  81       --count;
  82       if ((*dscan++ = *sscan++) == '\0')
  83         break;
  84     }
  85   while (count-- > 0)
  86     *dscan++ = '\0';
  87
  88   return dst0;
  89 #else
  90   char *dst = dst0;
  91   _CONST char *src = src0;
  92   long *aligned_dst;
  93   _CONST long *aligned_src;
  94
  95   /* If SRC and DEST is aligned and count large enough, then copy words.  */
  96   if (!UNALIGNED (src, dst) && !TOO_SMALL (count))
  97     {
  98       aligned_dst = (long*)dst;
  99       aligned_src = (long*)src;
 100
 101       /* SRC and DEST are both "long int" aligned, try to do "long int"
 102          sized copies.  */
 103       while (count >= sizeof (long int) && !DETECTNULL(*aligned_src))
 104         {
 105           count -= sizeof (long int);
 106           *aligned_dst++ = *aligned_src++;
 107         }
 108
 109       dst = (char*)aligned_dst;
 110       src = (char*)aligned_src;
 111     }
 112
 113   while (count > 0)
 114     {
 115       --count;
 116       if ((*dst++ = *src++) == '\0')
 117         break;
 118     }
 119
 120   while (count-- > 0)
 121     *dst++ = '\0';
 122
 123   return dst0;
 124 #endif /* not PREFER_SIZE_OVER_SPEED */
 125 }