LXR linux/arch/tile/lib/strchr

   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
  19char *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}
  64EXPORT_SYMBOL(strchr);
  65