LXR linux/arch/tile/lib/memchr

   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
  20void *memchr(const void *s, int c, size_t n)
  21{
  22        const uint64_t *last_word_ptr;
  23        const uint64_t *p;
  24        const char *last_byte_ptr;
  25        uintptr_t s_int;
  26        uint64_t goal, before_mask, v, bits;
  27        char *ret;
  28
  29        if (__builtin_expect(n == 0, 0)) {
  30                /* Don't dereference any memory if the array is empty. */
  31                return NULL;
  32        }
  33
  34        /* Get an aligned pointer. */
  35        s_int = (uintptr_t) s;
  36        p = (const uint64_t *)(s_int & -8);
  37
  38        /* Create eight copies of the byte for which we are looking. */
  39        goal = 0x0101010101010101ULL * (uint8_t) c;
  40
  41        /* Read the first word, but munge it so that bytes before the array
  42         * will not match goal.
  43         */
  44        before_mask = MASK(s_int);
  45        v = (*p | before_mask) ^ (goal & before_mask);
  46
  47        /* Compute the address of the last byte. */
  48        last_byte_ptr = (const char *)s + n - 1;
  49
  50        /* Compute the address of the word containing the last byte. */
  51        last_word_ptr = (const uint64_t *)((uintptr_t) last_byte_ptr & -8);
  52
  53        while ((bits = __insn_v1cmpeq(v, goal)) == 0) {
  54                if (__builtin_expect(p == last_word_ptr, 0)) {
  55                        /* We already read the last word in the array,
  56                         * so give up.
  57                         */
  58                        return NULL;
  59                }
  60                v = *++p;
  61        }
  62
  63        /* We found a match, but it might be in a byte past the end
  64         * of the array.
  65         */
  66        ret = ((char *)p) + (CFZ(bits) >> 3);
  67        return (ret <= last_byte_ptr) ? ret : NULL;
  68}
  69EXPORT_SYMBOL(memchr);
  70