sysdeps/tile/tilepro/strrchr.c

   1 /* Copyright (C) 2011-2015 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, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <string.h>
  20 #include <stdint.h>
  21
  22 char *
  23 strrchr (const char *s, int c)
  24 {
  25   /* Get an aligned pointer. */
  26   const uintptr_t s_int = (uintptr_t) s;
  27   const uint32_t *p = (const uint32_t *) (s_int & -4);
  28
  29   /* Create four copies of the byte for which we are looking. */
  30   const uint32_t goal = 0x01010101 * (uint8_t) c;
  31
  32   /* Read the first aligned word, but force bytes before the string to
  33      match neither zero nor goal (we make sure the high bit of each
  34      byte is 1, and the low 7 bits are all the opposite of the goal
  35      byte).  Note that this shift count expression works because we
  36      know shift counts are taken mod 32.  */
  37   const uint32_t before_mask = (1 << (s_int << 3)) - 1;
  38   uint32_t v = (*p | before_mask) ^ (goal & __insn_shrib (before_mask, 1));
  39   const char *found = NULL;
  40   uint32_t zero_matches, goal_matches;
  41   while (1)
  42     {
  43       /* Look for a terminating '\0'. */
  44       zero_matches = __insn_seqb (v, 0);
  45
  46       /* Look for the goal byte. */
  47       goal_matches = __insn_seqb (v, goal);
  48
  49       /* If we found the goal, record the last offset. */
  50       if (__builtin_expect (goal_matches != 0, 0))
  51         {
  52           if (__builtin_expect (zero_matches != 0, 0))
  53             {
  54               /* Clear any goal after the first zero. */
  55               int first_nul = __insn_ctz (zero_matches);
  56               /* The number of top bits we need to clear is
  57                  32 - (first_nul + 8).  */
  58               int shift_amt = (24 - first_nul);
  59               goal_matches <<= shift_amt;
  60               goal_matches >>= shift_amt;
  61             }
  62           if (__builtin_expect (goal_matches != 0, 1))
  63             found = ((char *) p) + 3 - (__insn_clz (goal_matches) >> 3);
  64         }
  65
  66       if (__builtin_expect (zero_matches != 0, 0))
  67         return (char *) found;
  68
  69       v = *++p;
  70     }
  71 }
  72 weak_alias (strrchr, rindex)
  73 libc_hidden_builtin_def (strrchr)