string/strncpy.c

   1 /* Copyright (C) 1991, 1997, 2003 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 Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the 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    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <string.h>
  20 #include <memcopy.h>
  21
  22 #undef strncpy
  23
  24 #ifndef STRNCPY
  25 #define STRNCPY strncpy
  26 #endif
  27
  28 char *
  29 STRNCPY (char *s1, const char *s2, size_t n)
  30 {
  31   reg_char c;
  32   char *s = s1;
  33
  34   --s1;
  35
  36   if (n >= 4)
  37     {
  38       size_t n4 = n >> 2;
  39
  40       for (;;)
  41         {
  42           c = *s2++;
  43           *++s1 = c;
  44           if (c == '\0')
  45             break;
  46           c = *s2++;
  47           *++s1 = c;
  48           if (c == '\0')
  49             break;
  50           c = *s2++;
  51           *++s1 = c;
  52           if (c == '\0')
  53             break;
  54           c = *s2++;
  55           *++s1 = c;
  56           if (c == '\0')
  57             break;
  58           if (--n4 == 0)
  59             goto last_chars;
  60         }
  61       n = n - (s1 - s) - 1;
  62       if (n == 0)
  63         return s;
  64       goto zero_fill;
  65     }
  66
  67  last_chars:
  68   n &= 3;
  69   if (n == 0)
  70     return s;
  71
  72   do
  73     {
  74       c = *s2++;
  75       *++s1 = c;
  76       if (--n == 0)
  77         return s;
  78     }
  79   while (c != '\0');
  80
  81  zero_fill:
  82   do
  83     *++s1 = '\0';
  84   while (--n > 0);
  85
  86   return s;
  87 }
  88 libc_hidden_builtin_def (strncpy)