1  /* Copyright (C) 1993, 1995-1997, 2002-2003, 2005-2007, 2009-2023 Free Software
       2   * Foundation, Inc.
       3  
       4     NOTE: The canonical source of this file is maintained with the GNU C Library.
       5     Bugs can be reported to bug-glibc@gnu.org.
       6  
       7     This file is free software: you can redistribute it and/or modify
       8     it under the terms of the GNU Lesser General Public License as
       9     published by the Free Software Foundation; either version 2.1 of the
      10     License, or (at your option) any later version.
      11  
      12     This file is distributed in the hope that it will be useful,
      13     but WITHOUT ANY WARRANTY; without even the implied warranty of
      14     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      15     GNU Lesser General Public License for more details.
      16  
      17     You should have received a copy of the GNU Lesser General Public License
      18     along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
      19  
      20  /* This is almost copied from strncpy.c, written by Torbjorn Granlund.  */
      21  
      22  #include <config.h>
      23  
      24  /* Specification.  */
      25  #include <string.h>
      26  
      27  #ifndef weak_alias
      28  # define __stpncpy stpncpy
      29  #endif
      30  
      31  /* Copy no more than N bytes of SRC to DST, returning a pointer past the
      32     last non-NUL byte written into DST.  */
      33  char *
      34  (__stpncpy) (char *dest, const char *src, size_t n)
      35  {
      36    char c;
      37    char *s = dest;
      38  
      39    if (n >= 4)
      40      {
      41        size_t n4 = n >> 2;
      42  
      43        for (;;)
      44          {
      45            c = *src++;
      46            *dest++ = c;
      47            if (c == '\0')
      48              break;
      49            c = *src++;
      50            *dest++ = c;
      51            if (c == '\0')
      52              break;
      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            if (--n4 == 0)
      62              goto last_chars;
      63          }
      64        n -= dest - s;
      65        goto zero_fill;
      66      }
      67  
      68   last_chars:
      69    n &= 3;
      70    if (n == 0)
      71      return dest;
      72  
      73    for (;;)
      74      {
      75        c = *src++;
      76        --n;
      77        *dest++ = c;
      78        if (c == '\0')
      79          break;
      80        if (n == 0)
      81          return dest;
      82      }
      83  
      84   zero_fill:
      85    while (n-- > 0)
      86      dest[n] = '\0';
      87  
      88    return dest - 1;
      89  }
      90  #ifdef weak_alias
      91  weak_alias (__stpncpy, stpncpy)
      92  #endif