arch/tile/lib/memchr_64.c

   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
  20 void *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 }
  69 EXPORT_SYMBOL(memchr);