sysdeps/tile/tilegx/strnlen.c

   1 /* Copyright (C) 2013 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Chris Metcalf <cmetcalf@tilera.com>, 2011.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <string.h>
  21 #include <stdint.h>
  22 #include "string-endian.h"
  23
  24 /* Find the length of S, but scan at most MAXLEN characters.  If no
  25    '\0' terminator is found in that many characters, return MAXLEN.  */
  26 size_t
  27 __strnlen (const char *s, size_t maxlen)
  28 {
  29   /* When maxlen is 0, can't read any bytes or it might cause a page fault.  */
  30   if (maxlen == 0)
  31     return 0;
  32
  33   /* Get an aligned pointer. */
  34   const uintptr_t s_int = (uintptr_t) s;
  35   const uint64_t *p = (const uint64_t *) (s_int & -8);
  36   size_t bytes_read = sizeof (*p) - (s_int & (sizeof (*p) - 1));
  37
  38   /* Read and MASK the first word. */
  39   uint64_t v = *p | MASK (s_int);
  40
  41   uint64_t bits;
  42   while ((bits = __insn_v1cmpeqi (v, 0)) == 0)
  43     {
  44       if (bytes_read >= maxlen)
  45         {
  46           /* Read maxlen bytes and didn't find the terminator. */
  47           return maxlen;
  48         }
  49       v = *++p;
  50       bytes_read += sizeof (v);
  51     }
  52
  53   /* Found '\0', check it is not larger than maxlen */
  54   size_t len = ((const char *) p) + (CFZ (bits) >> 3) - s;
  55   return (len < maxlen ? len : maxlen);
  56 }
  57 weak_alias (__strnlen, strnlen)
  58 libc_hidden_def (strnlen)