string/strncpy.c

   1 /* Copyright (C) 1991-2015 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, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <string.h>
  19 #include <memcopy.h>
  20
  21 #undef strncpy
  22
  23 #ifndef STRNCPY
  24 #define STRNCPY strncpy
  25 #endif
  26
  27 char *
  28 STRNCPY (char *s1, const char *s2, size_t n)
  29 {
  30   char c;
  31   char *s = s1;
  32
  33   --s1;
  34
  35   if (n >= 4)
  36     {
  37       size_t n4 = n >> 2;
  38
  39       for (;;)
  40         {
  41           c = *s2++;
  42           *++s1 = c;
  43           if (c == '\0')
  44             break;
  45           c = *s2++;
  46           *++s1 = c;
  47           if (c == '\0')
  48             break;
  49           c = *s2++;
  50           *++s1 = c;
  51           if (c == '\0')
  52             break;
  53           c = *s2++;
  54           *++s1 = c;
  55           if (c == '\0')
  56             break;
  57           if (--n4 == 0)
  58             goto last_chars;
  59         }
  60       s1++;
  61       n = n - (s1 - s);
  62       memset (s1, '\0', n);
  63       return s;
  64     }
  65
  66  last_chars:
  67   n &= 3;
  68   if (n == 0)
  69     return s;
  70
  71   do
  72     {
  73       c = *s2++;
  74       *++s1 = c;
  75       if (--n == 0)
  76         return s;
  77     }
  78   while (c != '\0');
  79
  80   memset (s1 + 1, '\0', n);
  81   return s;
  82 }
  83 libc_hidden_builtin_def (strncpy)