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
  19#undef strchr
  20
  21char *strchr(const char *s, int c)
  22{
  23        int z, g;
  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).
  36         *
  37         * Note that this shift count expression works because we know shift
  38         * counts are taken mod 32.
  39         */
  40        const uint32_t before_mask = (1 << (s_int << 3)) - 1;
  41        uint32_t v = (*p | before_mask) ^ (goal & __insn_shrib(before_mask, 1));
  42
  43        uint32_t zero_matches, goal_matches;
  44        while (1) {
  45                /* Look for a terminating '\0'. */
  46                zero_matches = __insn_seqb(v, 0);
  47
  48                /* Look for the goal byte. */
  49                goal_matches = __insn_seqb(v, goal);
  50
  51                if (__builtin_expect(zero_matches | goal_matches, 0))
  52                        break;
  53
  54                v = *++p;
  55        }
  56
  57        z = __insn_ctz(zero_matches);
  58        g = __insn_ctz(goal_matches);
  59
  60        /* If we found c before '\0' we got a match. Note that if c == '\0'
  61         * then g == z, and we correctly return the address of the '\0'
  62         * rather than NULL.
  63         */
  64        return (g <= z) ? ((char *)p) + (g >> 3) : NULL;
  65}
  66EXPORT_SYMBOL(strchr);
  67