lib/stpncpy.c

   1 /* Copyright (C) 1993, 1995-1997, 2002-2003, 2005-2007, 2009-2019 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 program is free software: you can redistribute it and/or modify it
   8    under the terms of the GNU General Public License as published by the
   9    Free Software Foundation; either version 3 of the License, or any
  10    later version.
  11
  12    This program 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 General Public License for more details.
  16
  17    You should have received a copy of the GNU 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