LXR linux/arch/tile/lib/memchr

   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
  19void *memchr(const void *s, int c, size_t n)
  20{
  21        const uint32_t *last_word_ptr;
  22        const uint32_t *p;
  23        const char *last_byte_ptr;
  24        uintptr_t s_int;
  25        uint32_t goal, before_mask, v, bits;
  26        char *ret;
  27
  28        if (__builtin_expect(n == 0, 0)) {
  29                /* Don't dereference any memory if the array is empty. */
  30                return NULL;
  31        }
  32
  33        /* Get an aligned pointer. */
  34        s_int = (uintptr_t) s;
  35        p = (const uint32_t *)(s_int & -4);
  36
  37        /* Create four copies of the byte for which we are looking. */
  38        goal = 0x01010101 * (uint8_t) c;
  39
  40        /* Read the first word, but munge it so that bytes before the array
  41         * will not match goal.
  42         *
  43         * Note that this shift count expression works because we know
  44         * shift counts are taken mod 32.
  45         */
  46        before_mask = (1 << (s_int << 3)) - 1;
  47        v = (*p | before_mask) ^ (goal & before_mask);
  48
  49        /* Compute the address of the last byte. */
  50        last_byte_ptr = (const char *)s + n - 1;
  51
  52        /* Compute the address of the word containing the last byte. */
  53        last_word_ptr = (const uint32_t *)((uintptr_t) last_byte_ptr & -4);
  54
  55        while ((bits = __insn_seqb(v, goal)) == 0) {
  56                if (__builtin_expect(p == last_word_ptr, 0)) {
  57                        /* We already read the last word in the array,
  58                         * so give up.
  59                         */
  60                        return NULL;
  61                }
  62                v = *++p;
  63        }
  64
  65        /* We found a match, but it might be in a byte past the end
  66         * of the array.
  67         */
  68        ret = ((char *)p) + (__insn_ctz(bits) >> 3);
  69        return (ret <= last_byte_ptr) ? ret : NULL;
  70}
  71EXPORT_SYMBOL(memchr);
  72