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

   1 /*
   2 FUNCTION
   3         <<strncat>>---concatenate strings
   4
   5 INDEX
   6         strncat
   7
   8 ANSI_SYNOPSIS
   9         #include <string.h>
  10         char *strncat(char *<[dst]>, const char *<[src]>, size_t <[length]>);
  11
  12 TRAD_SYNOPSIS
  13         #include <string.h>
  14         char *strncat(<[dst]>, <[src]>, <[length]>)
  15         char *<[dst]>;
  16         char *<[src]>;
  17         size_t <[length]>;
  18
  19 DESCRIPTION
  20         <<strncat>> appends not more than <[length]> characters from
  21         the string pointed to by <[src]> (including the terminating
  22         null character) to the end of the string pointed to by
  23         <[dst]>.  The initial character of <[src]> overwrites the null
  24         character at the end of <[dst]>.  A terminating null character
  25         is always appended to the result
  26
  27 WARNINGS
  28         Note that a null is always appended, so that if the copy is
  29         limited by the <[length]> argument, the number of characters
  30         appended to <[dst]> is <<n + 1>>.
  31
  32
  33 RETURNS
  34         This function returns the initial value of <[dst]>
  35
  36 PORTABILITY
  37 <<strncat>> is ANSI C.
  38
  39 <<strncat>> requires no supporting OS subroutines.
  40
  41 QUICKREF
  42         strncat ansi pure
  43 */
  44
  45 #include <string.h>
  46 #include <limits.h>
  47
  48 /* Nonzero if X is aligned on a "long" boundary.  */
  49 #define ALIGNED(X) \
  50   (((long)X & (sizeof (long) - 1)) == 0)
  51
  52 #if LONG_MAX == 2147483647L
  53 #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
  54 #else
  55 #if LONG_MAX == 9223372036854775807L
  56 /* Nonzero if X (a long int) contains a NULL byte. */
  57 #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
  58 #else
  59 #error long int is not a 32bit or 64bit type.
  60 #endif
  61 #endif
  62
  63 #ifndef DETECTNULL
  64 #error long int is not a 32bit or 64bit byte
  65 #endif
  66
  67 char *
  68 _DEFUN (strncat, (s1, s2, n),
  69         char *s1 _AND
  70         _CONST char *s2 _AND
  71         size_t n)
  72 {
  73 #if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
  74   char *s = s1;
  75
  76   while (*s1)
  77     s1++;
  78   while (n-- != 0 && (*s1++ = *s2++))
  79     {
  80       if (n == 0)
  81         *s1 = '\0';
  82     }
  83
  84   return s;
  85 #else
  86   char *s = s1;
  87
  88   /* Skip over the data in s1 as quickly as possible.  */
  89   if (ALIGNED (s1))
  90     {
  91       unsigned long *aligned_s1 = (unsigned long *)s1;
  92       while (!DETECTNULL (*aligned_s1))
  93         aligned_s1++;
  94
  95       s1 = (char *)aligned_s1;
  96     }
  97
  98   while (*s1)
  99     s1++;
 100
 101   /* s1 now points to the its trailing null character, now copy
 102      up to N bytes from S2 into S1 stopping if a NULL is encountered
 103      in S2.
 104
 105      It is not safe to use strncpy here since it copies EXACTLY N
 106      characters, NULL padding if necessary.  */
 107   while (n-- != 0 && (*s1++ = *s2++))
 108     {
 109       if (n == 0)
 110         *s1 = '\0';
 111     }
 112
 113   return s;
 114 #endif /* not PREFER_SIZE_OVER_SPEED */
 115 }