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stpncpy.c

/* Copyright (C) 1993, 1995-1997, 2002-2003, 2005-2007 Free Software Foundation, Inc.

   NOTE: The canonical source of this file is maintained with the GNU C Library.
   Bugs can be reported to bug-glibc@gnu.org.

   This program is free software: you can redistribute it and/or modify it
   under the terms of the GNU General Public License as published by the
   Free Software Foundation; either version 3 of the License, or any
   later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

/* This is almost copied from strncpy.c, written by Torbjorn Granlund.  */

#include <config.h>

/* Specification.  */
#include <string.h>

#ifndef weak_alias
# define __stpncpy stpncpy
#endif

/* Copy no more than N bytes of SRC to DST, returning a pointer past the
   last non-NUL byte written into DST.  */
char *
__stpncpy (char *dest, const char *src, size_t n)
{
  char c;
  char *s = dest;

  if (n >= 4)
    {
      size_t n4 = n >> 2;

      for (;;)
      {
        c = *src++;
        *dest++ = c;
        if (c == '\0')
          break;
        c = *src++;
        *dest++ = c;
        if (c == '\0')
          break;
        c = *src++;
        *dest++ = c;
        if (c == '\0')
          break;
        c = *src++;
        *dest++ = c;
        if (c == '\0')
          break;
        if (--n4 == 0)
          goto last_chars;
      }
      n -= dest - s;
      goto zero_fill;
    }

 last_chars:
  n &= 3;
  if (n == 0)
    return dest;

  for (;;)
    {
      c = *src++;
      --n;
      *dest++ = c;
      if (c == '\0')
      break;
      if (n == 0)
      return dest;
    }

 zero_fill:
  while (n-- > 0)
    dest[n] = '\0';

  return dest - 1;
}
#ifdef weak_alias
weak_alias (__stpncpy, stpncpy)
#endif

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