string/stpncpy.c

   1 /* Copyright (C) 1993, 1995, 1996, 1997, 2002 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, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 /* This is almost copied from strncpy.c, written by Torbjorn Granlund.  */
  20
  21 #ifdef HAVE_CONFIG_H
  22 # include <config.h>
  23 #endif
  24
  25 #ifdef _LIBC
  26 # include <string.h>
  27 #else
  28 # include <sys/types.h>
  29 #endif
  30
  31 #ifndef weak_alias
  32 # define __stpncpy stpncpy
  33 #endif
  34
  35 /* Copy no more than N characters of SRC to DEST, returning the address of
  36    the terminating '\0' in DEST, if any, or else DEST + N.  */
  37 char *
  38 __stpncpy (dest, src, n)
  39      char *dest;
  40      const char *src;
  41      size_t n;
  42 {
  43   char c;
  44   char *s = dest;
  45
  46   if (n >= 4)
  47     {
  48       size_t n4 = n >> 2;
  49
  50       for (;;)
  51         {
  52           c = *src++;
  53           *dest++ = c;
  54           if (c == '\0')
  55             break;
  56           c = *src++;
  57           *dest++ = c;
  58           if (c == '\0')
  59             break;
  60           c = *src++;
  61           *dest++ = c;
  62           if (c == '\0')
  63             break;
  64           c = *src++;
  65           *dest++ = c;
  66           if (c == '\0')
  67             break;
  68           if (--n4 == 0)
  69             goto last_chars;
  70         }
  71       n -= dest - s;
  72       goto zero_fill;
  73     }
  74
  75  last_chars:
  76   n &= 3;
  77   if (n == 0)
  78     return dest;
  79
  80   for (;;)
  81     {
  82       c = *src++;
  83       --n;
  84       *dest++ = c;
  85       if (c == '\0')
  86         break;
  87       if (n == 0)
  88         return dest;
  89     }
  90
  91  zero_fill:
  92   while (n-- > 0)
  93     dest[n] = '\0';
  94
  95   return dest - 1;
  96 }
  97 #ifdef weak_alias
  98 libc_hidden_def (__stpncpy)
  99 weak_alias (__stpncpy, stpncpy)
 100 #endif