lib/stpncpy.c

/* Copyright (C) 1993, 1995-1997, 2002-2003, 2005-2007, 2009-2026 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 file is free software: you can redistribute it and/or modify
   it under the terms of the GNU Lesser General Public License as
   published by the Free Software Foundation; either version 2.1 of the
   License, or (at your option) any later version.

   This file 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 Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License
   along with this program.  If not, see <https://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 *s = dest;

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

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