string/stpncpy.c

   1 /* Copyright (C) 1993-2015 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 #ifdef HAVE_CONFIG_H
  21 # include <config.h>
  22 #endif
  23
  24 #ifdef _LIBC
  25 # include <string.h>
  26 #else
  27 # include <sys/types.h>
  28 #endif
  29
  30 #ifndef STPNCPY
  31 # ifdef weak_alias
  32 #  define STPNCPY       __stpncpy
  33 weak_alias (__stpncpy, stpncpy)
  34 # else
  35 #  define STPNCPY       stpncpy
  36 # endif
  37 #endif
  38
  39 /* Copy no more than N characters of SRC to DEST, returning the address of
  40    the terminating '\0' in DEST, if any, or else DEST + N.  */
  41 char *
  42 STPNCPY (char *dest, const char *src, size_t n)
  43 {
  44   char c;
  45   char *s = dest;
  46
  47   if (n >= 4)
  48     {
  49       size_t n4 = n >> 2;
  50
  51       for (;;)
  52         {
  53           c = *src++;
  54           *dest++ = c;
  55           if (c == '\0')
  56             break;
  57           c = *src++;
  58           *dest++ = c;
  59           if (c == '\0')
  60             break;
  61           c = *src++;
  62           *dest++ = c;
  63           if (c == '\0')
  64             break;
  65           c = *src++;
  66           *dest++ = c;
  67           if (c == '\0')
  68             break;
  69           if (--n4 == 0)
  70             goto last_chars;
  71         }
  72       n -= dest - s;
  73       goto zero_fill;
  74     }
  75
  76  last_chars:
  77   n &= 3;
  78   if (n == 0)
  79     return dest;
  80
  81   for (;;)
  82     {
  83       c = *src++;
  84       --n;
  85       *dest++ = c;
  86       if (c == '\0')
  87         break;
  88       if (n == 0)
  89         return dest;
  90     }
  91
  92  zero_fill:
  93   while (n-- > 0)
  94     dest[n] = '\0';
  95
  96   return dest - 1;
  97 }
  98 #ifdef weak_alias
  99 libc_hidden_def (__stpncpy)
 100 #endif