sysdeps/generic/stpncpy.c

   1 /* Copyright (C) 1993, 1995, 1996 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 terminating '\0' in DEST, if any, or else DEST + N.  */
  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   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 }
  85
  86 weak_alias (__stpncpy, stpncpy)