LXR linux/arch/tile/lib/strchr

   1/*
   2 * Copyright 2011 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#include "string-endian.h"
  19
  20char *strchr(const char *s, int c)
  21{
  22        int z, g;
  23
  24        /* Get an aligned pointer. */
  25        const uintptr_t s_int = (uintptr_t) s;
  26        const uint64_t *p = (const uint64_t *)(s_int & -8);
  27
  28        /* Create eight copies of the byte for which we are looking. */
  29        const uint64_t goal = 0x0101010101010101ULL * (uint8_t) c;
  30
  31        /* Read the first aligned word, but force bytes before the string to
  32         * match neither zero nor goal (we make sure the high bit of each
  33         * byte is 1, and the low 7 bits are all the opposite of the goal
  34         * byte).
  35         */
  36        const uint64_t before_mask = MASK(s_int);
  37        uint64_t v = (*p | before_mask) ^ (goal & __insn_v1shrui(before_mask, 1));
  38
  39        uint64_t zero_matches, goal_matches;
  40        while (1) {
  41                /* Look for a terminating '\0'. */
  42                zero_matches = __insn_v1cmpeqi(v, 0);
  43
  44                /* Look for the goal byte. */
  45                goal_matches = __insn_v1cmpeq(v, goal);
  46
  47                if (__builtin_expect((zero_matches | goal_matches) != 0, 0))
  48                        break;
  49
  50                v = *++p;
  51        }
  52
  53        z = CFZ(zero_matches);
  54        g = CFZ(goal_matches);
  55
  56        /* If we found c before '\0' we got a match. Note that if c == '\0'
  57         * then g == z, and we correctly return the address of the '\0'
  58         * rather than NULL.
  59         */
  60        return (g <= z) ? ((char *)p) + (g >> 3) : NULL;
  61}
  62EXPORT_SYMBOL(strchr);
  63