sysdeps/generic/strncpy.c

   1 /* Copyright (C) 1991, 1997 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 not,
  16    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17    Boston, MA 02111-1307, USA.  */
  18
  19 #include <string.h>
  20 #include <memcopy.h>
  21
  22
  23 char *
  24 strncpy (s1, s2, n)
  25      char *s1;
  26      const char *s2;
  27      size_t n;
  28 {
  29   reg_char c;
  30   char *s = s1;
  31
  32   --s1;
  33
  34   if (n >= 4)
  35     {
  36       size_t n4 = n >> 2;
  37
  38       for (;;)
  39         {
  40           c = *s2++;
  41           *++s1 = c;
  42           if (c == '\0')
  43             break;
  44           c = *s2++;
  45           *++s1 = c;
  46           if (c == '\0')
  47             break;
  48           c = *s2++;
  49           *++s1 = c;
  50           if (c == '\0')
  51             break;
  52           c = *s2++;
  53           *++s1 = c;
  54           if (c == '\0')
  55             break;
  56           if (--n4 == 0)
  57             goto last_chars;
  58         }
  59       n = n - (s1 - s) - 1;
  60       if (n == 0)
  61         return s;
  62       goto zero_fill;
  63     }
  64
  65  last_chars:
  66   n &= 3;
  67   if (n == 0)
  68     return s;
  69
  70   do
  71     {
  72       c = *s2++;
  73       *++s1 = c;
  74       if (--n == 0)
  75         return s;
  76     }
  77   while (c != '\0');
  78
  79  zero_fill:
  80   do
  81     *++s1 = '\0';
  82   while (--n > 0);
  83
  84   return s;
  85 }