debug/stpncpy_chk.c

   1 /* Copyright (C) 1993-2013 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 /* This is almost copied from strncpy.c, written by Torbjorn Granlund.  */
  19
  20 #include <string.h>
  21
  22
  23 /* Copy no more than N characters of SRC to DEST, returning the address of
  24    the terminating '\0' in DEST, if any, or else DEST + N.  */
  25 char *
  26 __stpncpy_chk (char *dest, const char *src, size_t n, size_t destlen)
  27 {
  28   char c;
  29   char *s = dest;
  30
  31   if (__builtin_expect (destlen < n, 0))
  32     __chk_fail ();
  33
  34   if (n >= 4)
  35     {
  36       size_t n4 = n >> 2;
  37
  38       for (;;)
  39         {
  40           c = *src++;
  41           *dest++ = c;
  42           if (c == '\0')
  43             break;
  44           c = *src++;
  45           *dest++ = c;
  46           if (c == '\0')
  47             break;
  48           c = *src++;
  49           *dest++ = c;
  50           if (c == '\0')
  51             break;
  52           c = *src++;
  53           *dest++ = c;
  54           if (c == '\0')
  55             break;
  56           if (--n4 == 0)
  57             goto last_chars;
  58         }
  59       n -= dest - s;
  60       goto zero_fill;
  61     }
  62
  63  last_chars:
  64   n &= 3;
  65   if (n == 0)
  66     return dest;
  67
  68   for (;;)
  69     {
  70       c = *src++;
  71       --n;
  72       *dest++ = c;
  73       if (c == '\0')
  74         break;
  75       if (n == 0)
  76         return dest;
  77     }
  78
  79  zero_fill:
  80   while (n-- > 0)
  81     dest[n] = '\0';
  82
  83   return dest - 1;
  84 }