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
  19 void *memchr(const void *s, int c, size_t n)
  20 {
  21         const uint64_t *last_word_ptr;
  22         const uint64_t *p;
  23         const char *last_byte_ptr;
  24         uintptr_t s_int;
  25         uint64_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 uint64_t *)(s_int & -8);
  36
  37         /* Create eight copies of the byte for which we are looking. */
  38         goal = 0x0101010101010101ULL * (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 64.
  45          */
  46         before_mask = (1ULL << (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 uint64_t *)((uintptr_t) last_byte_ptr & -8);
  54
  55         while ((bits = __insn_v1cmpeq(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 }
  71 EXPORT_SYMBOL(memchr);