sysdeps/generic/strncat.c

   1 /* Copyright (C) 1991 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3
   4 The GNU C Library is free software; you can redistribute it and/or
   5 modify it under the terms of the GNU Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 License, or (at your option) any later version.
   8
   9 The GNU C Library is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <ansidecl.h>
  20 #include <string.h>
  21 #include <memcopy.h>
  22
  23 char *
  24 DEFUN(strncat, (s1, s2, n), char *s1 AND CONST char *s2 AND size_t n)
  25 {
  26   reg_char c;
  27   char *s = s1;
  28
  29   /* Find the end of S1.  */
  30   do
  31     c = *s1++;
  32   while (c != '\0');
  33
  34   /* Make S1 point before next character, so we can increment
  35      it while memory is read (wins on pipelined cpus).  */
  36   s1 -= 2;
  37
  38   if (n >= 4)
  39     {
  40       size_t n4 = n >> 2;
  41       do
  42         {
  43           c = *s2++;
  44           *++s1 = c;
  45           if (c == '\0')
  46             return s;
  47           c = *s2++;
  48           *++s1 = c;
  49           if (c == '\0')
  50             return s;
  51           c = *s2++;
  52           *++s1 = c;
  53           if (c == '\0')
  54             return s;
  55           c = *s2++;
  56           *++s1 = c;
  57           if (c == '\0')
  58             return s;
  59         } while (--n4 > 0);
  60       n &= 3;
  61     }
  62
  63   while (n > 0)
  64     {
  65       c = *s2++;
  66       *++s1 = c;
  67       if (c == '\0')
  68         return s;
  69       n--;
  70     }
  71
  72   if (c != '\0')
  73     *++s1 = '\0';
  74
  75   return s;
  76 }