sysdeps/tile/strnlen.c

   1 /* Copyright (C) 2013-2018 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <string.h>
  19 #include <stdint.h>
  20 #include "string-endian.h"
  21
  22 /* Find the length of S, but scan at most MAXLEN characters.  If no
  23    '\0' terminator is found in that many characters, return MAXLEN.  */
  24 size_t
  25 __strnlen (const char *s, size_t maxlen)
  26 {
  27   /* When maxlen is 0, can't read any bytes or it might cause a page fault.  */
  28   if (maxlen == 0)
  29     return 0;
  30
  31   /* Get an aligned pointer. */
  32   const uintptr_t s_int = (uintptr_t) s;
  33   const uint64_t *p = (const uint64_t *) (s_int & -8);
  34   size_t bytes_read = sizeof (*p) - (s_int & (sizeof (*p) - 1));
  35
  36   /* Read and MASK the first word. */
  37   uint64_t v = *p | MASK (s_int);
  38
  39   uint64_t bits;
  40   while ((bits = v1cmpeqi (v, 0)) == 0)
  41     {
  42       if (bytes_read >= maxlen)
  43         {
  44           /* Read maxlen bytes and didn't find the terminator. */
  45           return maxlen;
  46         }
  47       v = *++p;
  48       bytes_read += sizeof (v);
  49     }
  50
  51   /* Found '\0', check it is not larger than maxlen */
  52   size_t len = ((const char *) p) + (CFZ (bits) >> 3) - s;
  53   return (len < maxlen ? len : maxlen);
  54 }
  55 libc_hidden_def (__strnlen)
  56 weak_alias (__strnlen, strnlen)
  57 libc_hidden_def (strnlen)