sysdeps/generic/strncpy.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(strncpy, (s1, s2, n), char *s1 AND CONST char *s2 AND size_t n)
  25 {
  26   reg_char c;
  27   char *s = s1;
  28
  29   --s1;
  30
  31   if (n >= 4)
  32     {
  33       size_t n4 = n >> 2;
  34
  35       for (;;)
  36         {
  37           c = *s2++;
  38           *++s1 = c;
  39           if (c == '\0')
  40             break;
  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           if (--n4 == 0)
  54             goto last_chars;
  55         }
  56       n = n - (s1 - s) - 1;
  57       if (n == 0)
  58         return s;
  59       goto zero_fill;
  60     }
  61
  62  last_chars:
  63   n &= 3;
  64   if (n == 0)
  65     return s;
  66
  67   do
  68     {
  69       c = *s2++;
  70       *++s1 = c;
  71       if (--n == 0)
  72         return s;
  73     }
  74   while (c != '\0');
  75
  76  zero_fill:
  77   do
  78     *++s1 = '\0';
  79   while (--n > 0);
  80
  81   return s;
  82 }