libc/string/strncpy.c

   1 /*
   2  *  ZeX/OS
   3  *  Copyright (C) 2007  Tomas 'ZeXx86' Jedrzejek (zexx86@zexos.org)
   4  *  Copyright (C) 2008  Tomas 'ZeXx86' Jedrzejek (zexx86@zexos.org)
   5  *
   6  *  This program is free software: you can redistribute it and/or modify
   7  *  it under the terms of the GNU General Public License as published by
   8  *  the Free Software Foundation, either version 3 of the License, or
   9  *  (at your option) any later version.
  10  *
  11  *  This program is distributed in the hope that it will be useful,
  12  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  *  GNU General Public License for more details.
  15  *
  16  *  You should have received a copy of the GNU General Public License
  17  *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18  */
  19
  20
  21 #include <string.h>
  22
  23 char *strncpy (char *s1, const char *s2, size_t n)
  24 {
  25         register char c;
  26         char *s = s1;
  27
  28         -- s1;
  29
  30         if (n >= 4)
  31         {
  32                 size_t n4 = n >> 2;
  33
  34                 for (;;)
  35                 {
  36                         c = *s2 ++;
  37                         *++s1 = c;
  38
  39                         if (c == '\0')
  40                                 break;
  41
  42                         c = *s2 ++;
  43
  44                         *++s1 = c;
  45                         if (c == '\0')
  46                                 break;
  47
  48                         c = *s2 ++;
  49                         *++s1 = c;
  50
  51                         if (c == '\0')
  52                                 break;
  53
  54                         c = *s2 ++;
  55                         *++s1 = c;
  56
  57                         if (c == '\0')
  58                                 break;
  59
  60                         if (--n4 == 0)
  61                                 goto last_chars;
  62                 }
  63
  64                 n = n - (s1 - s) - 1;
  65
  66                 if (n == 0)
  67                         return s;
  68
  69                 goto zero_fill;
  70         }
  71
  72 last_chars:
  73         n &= 3;
  74         if (n == 0)
  75         return s;
  76
  77         do
  78         {
  79                 c = *s2 ++;
  80                 *++s1 = c;
  81                 if (-- n == 0)
  82                         return s;
  83         }
  84
  85         while (c != '\0');
  86
  87 zero_fill:
  88         do
  89                 *++s1 = '\0';
  90         while (-- n > 0);
  91
  92         return s;
  93 }
  94