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glibc  2.9
strncpy.c
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00001 /* Copyright (C) 1991, 1997, 2003 Free Software Foundation, Inc.
00002    This file is part of the GNU C Library.
00003 
00004    The GNU C Library is free software; you can redistribute it and/or
00005    modify it under the terms of the GNU Lesser General Public
00006    License as published by the Free Software Foundation; either
00007    version 2.1 of the License, or (at your option) any later version.
00008 
00009    The GNU C Library is distributed in the hope that it will be useful,
00010    but WITHOUT ANY WARRANTY; without even the implied warranty of
00011    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00012    Lesser General Public License for more details.
00013 
00014    You should have received a copy of the GNU Lesser General Public
00015    License along with the GNU C Library; if not, write to the Free
00016    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00017    02111-1307 USA.  */
00018 
00019 #include <string.h>
00020 #include <memcopy.h>
00021 
00022 #undef strncpy
00023 
00024 char *
00025 strncpy (s1, s2, n)
00026      char *s1;
00027      const char *s2;
00028      size_t n;
00029 {
00030   reg_char c;
00031   char *s = s1;
00032 
00033   --s1;
00034 
00035   if (n >= 4)
00036     {
00037       size_t n4 = n >> 2;
00038 
00039       for (;;)
00040        {
00041          c = *s2++;
00042          *++s1 = c;
00043          if (c == '\0')
00044            break;
00045          c = *s2++;
00046          *++s1 = c;
00047          if (c == '\0')
00048            break;
00049          c = *s2++;
00050          *++s1 = c;
00051          if (c == '\0')
00052            break;
00053          c = *s2++;
00054          *++s1 = c;
00055          if (c == '\0')
00056            break;
00057          if (--n4 == 0)
00058            goto last_chars;
00059        }
00060       n = n - (s1 - s) - 1;
00061       if (n == 0)
00062        return s;
00063       goto zero_fill;
00064     }
00065 
00066  last_chars:
00067   n &= 3;
00068   if (n == 0)
00069     return s;
00070 
00071   do
00072     {
00073       c = *s2++;
00074       *++s1 = c;
00075       if (--n == 0)
00076        return s;
00077     }
00078   while (c != '\0');
00079 
00080  zero_fill:
00081   do
00082     *++s1 = '\0';
00083   while (--n > 0);
00084 
00085   return s;
00086 }
00087 libc_hidden_builtin_def (strncpy)