sysdeps/generic/stpncpy.c

   1 /* Copyright (C) 1993, 1995 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 /* This is almost copied from strncpy.c, written by Torbjorn Granlund.  */
  20
  21 #include <ansidecl.h>
  22 #include <string.h>
  23 #include <memcopy.h>
  24
  25
  26 /* Copy no more than N characters of SRC to DEST, returning the address of
  27    the last character written into DEST.  */
  28 char *
  29 DEFUN(__stpncpy, (dest, src, n), char *dest AND CONST char *src AND size_t n)
  30 {
  31   reg_char c;
  32   char *s = dest;
  33
  34   --dest;
  35
  36   if (n >= 4)
  37     {
  38       size_t n4 = n >> 2;
  39
  40       for (;;)
  41         {
  42           c = *src++;
  43           *++dest = c;
  44           if (c == '\0')
  45             break;
  46           c = *src++;
  47           *++dest = c;
  48           if (c == '\0')
  49             break;
  50           c = *src++;
  51           *++dest = c;
  52           if (c == '\0')
  53             break;
  54           c = *src++;
  55           *++dest = c;
  56           if (c == '\0')
  57             break;
  58           if (--n4 == 0)
  59             goto last_chars;
  60         }
  61       n = n - (dest - s) - 1;
  62       if (n == 0)
  63         return dest;
  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 = *src++;
  75       *++dest = c;
  76       if (--n == 0)
  77         return dest;
  78     }
  79   while (c != '\0');
  80
  81  zero_fill:
  82   do
  83     *++dest = '\0';
  84   while (--n > 0);
  85
  86   return dest;
  87 }
  88
  89 weak_alias (__stpncpy, stpncpy)