arch/tile/lib/strchr_32.c

   1 /*
   2  * Copyright 2010 Tilera Corporation. All Rights Reserved.
   3  *
   4  *   This program is free software; you can redistribute it and/or
   5  *   modify it under the terms of the GNU General Public License
   6  *   as published by the Free Software Foundation, version 2.
   7  *
   8  *   This program is distributed in the hope that it will be useful, but
   9  *   WITHOUT ANY WARRANTY; without even the implied warranty of
  10  *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
  11  *   NON INFRINGEMENT.  See the GNU General Public License for
  12  *   more details.
  13  */
  14
  15 #include <linux/types.h>
  16 #include <linux/string.h>
  17 #include <linux/module.h>
  18
  19 char *strchr(const char *s, int c)
  20 {
  21         int z, g;
  22
  23         /* Get an aligned pointer. */
  24         const uintptr_t s_int = (uintptr_t) s;
  25         const uint32_t *p = (const uint32_t *)(s_int & -4);
  26
  27         /* Create four copies of the byte for which we are looking. */
  28         const uint32_t goal = 0x01010101 * (uint8_t) c;
  29
  30         /* Read the first aligned word, but force bytes before the string to
  31          * match neither zero nor goal (we make sure the high bit of each
  32          * byte is 1, and the low 7 bits are all the opposite of the goal
  33          * byte).
  34          *
  35          * Note that this shift count expression works because we know shift
  36          * counts are taken mod 32.
  37          */
  38         const uint32_t before_mask = (1 << (s_int << 3)) - 1;
  39         uint32_t v = (*p | before_mask) ^ (goal & __insn_shrib(before_mask, 1));
  40
  41         uint32_t zero_matches, goal_matches;
  42         while (1) {
  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 (__builtin_expect(zero_matches | goal_matches, 0))
  50                         break;
  51
  52                 v = *++p;
  53         }
  54
  55         z = __insn_ctz(zero_matches);
  56         g = __insn_ctz(goal_matches);
  57
  58         /* If we found c before '\0' we got a match. Note that if c == '\0'
  59          * then g == z, and we correctly return the address of the '\0'
  60          * rather than NULL.
  61          */
  62         return (g <= z) ? ((char *)p) + (g >> 3) : NULL;
  63 }
  64 EXPORT_SYMBOL(strchr);