newlib/libc/string/strcat.c

   1 /*
   2 FUNCTION
   3         <<strcat>>---concatenate strings
   4
   5 INDEX
   6         strcat
   7
   8 SYNOPSIS
   9         #include <string.h>
  10         char *strcat(char *restrict <[dst]>, const char *restrict <[src]>);
  11
  12 DESCRIPTION
  13         <<strcat>> appends a copy of the string pointed to by <[src]>
  14         (including the terminating null character) to the end of the
  15         string pointed to by <[dst]>.  The initial character of
  16         <[src]> overwrites the null character at the end of <[dst]>.
  17
  18 RETURNS
  19         This function returns the initial value of <[dst]>
  20
  21 PORTABILITY
  22 <<strcat>> is ANSI C.
  23
  24 <<strcat>> requires no supporting OS subroutines.
  25
  26 QUICKREF
  27         strcat ansi pure
  28 */
  29
  30 #include <string.h>
  31 #include <limits.h>
  32
  33 /* Nonzero if X is aligned on a "long" boundary.  */
  34 #define ALIGNED(X) \
  35   (((long)X & (sizeof (long) - 1)) == 0)
  36
  37 #if LONG_MAX == 2147483647L
  38 #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
  39 #else
  40 #if LONG_MAX == 9223372036854775807L
  41 /* Nonzero if X (a long int) contains a NULL byte. */
  42 #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
  43 #else
  44 #error long int is not a 32bit or 64bit type.
  45 #endif
  46 #endif
  47
  48 #ifndef DETECTNULL
  49 #error long int is not a 32bit or 64bit byte
  50 #endif
  51
  52
  53 /*SUPPRESS 560*/
  54 /*SUPPRESS 530*/
  55
  56 char *
  57 strcat (char *__restrict s1,
  58         const char *__restrict s2)
  59 {
  60 #if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
  61   char *s = s1;
  62
  63   while (*s1)
  64     s1++;
  65
  66   while (*s1++ = *s2++)
  67     ;
  68   return s;
  69 #else
  70   char *s = s1;
  71
  72
  73   /* Skip over the data in s1 as quickly as possible.  */
  74   if (ALIGNED (s1))
  75     {
  76       unsigned long *aligned_s1 = (unsigned long *)s1;
  77       while (!DETECTNULL (*aligned_s1))
  78         aligned_s1++;
  79
  80       s1 = (char *)aligned_s1;
  81     }
  82
  83   while (*s1)
  84     s1++;
  85
  86   /* s1 now points to the its trailing null character, we can
  87      just use strcpy to do the work for us now.
  88
  89      ?!? We might want to just include strcpy here.
  90      Also, this will cause many more unaligned string copies because
  91      s1 is much less likely to be aligned.  I don't know if its worth
  92      tweaking strcpy to handle this better.  */
  93   strcpy (s1, s2);
  94
  95   return s;
  96 #endif /* not PREFER_SIZE_OVER_SPEED */
  97 }