lib/libc/string/wcscspn_bloom.h

   1 /*      $NetBSD: wcscspn_bloom.h,v 1.4 2011/11/25 17:48:22 joerg Exp $  */
   2
   3 /*-
   4  * Copyright (c) 2011 Joerg Sonnenberger,
   5  * All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  19  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  26  * SUCH DAMAGE.
  27  */
  28
  29 /*
  30  * Bloom filter for fast test if a given character is part of the reject set.
  31  * The test may have false positives, but doesn't have false negatives.
  32  * The first hash function is designed to be very fast to evaluate.
  33  * It is collision free if the input is part of the same European language
  34  * and shouldn't be too bad even other input.  The second hash function
  35  * tries to provide a much better mixing, but involves the slower
  36  * multiplication.
  37  */
  38
  39 #include <limits.h>
  40
  41 #define BLOOM_SIZE              64
  42 #define BLOOM_ARRAY_SIZE        (BLOOM_SIZE / sizeof(size_t))
  43 #define BLOOM_BITS              (BLOOM_SIZE * CHAR_BIT)
  44 #define BLOOM_DIV               (sizeof(size_t) * CHAR_BIT)
  45
  46 static inline size_t
  47 wcscspn_bloom1(size_t x)
  48 {
  49         return x % BLOOM_BITS;
  50 }
  51
  52 static inline size_t
  53 wcscspn_bloom2(size_t x)
  54 {
  55         return (size_t)((uint32_t)(x * 2654435761U) /
  56             (0x100000000ULL / BLOOM_BITS));
  57 }
  58
  59 static inline void
  60 wcsspn_bloom_init(size_t *bloom, const wchar_t *charset)
  61 {
  62         size_t val;
  63
  64         memset(bloom, 0, BLOOM_SIZE);
  65         do {
  66                 val = wcscspn_bloom1((size_t)*charset);
  67                 bloom[val / BLOOM_DIV] |= (size_t)1 << (val % BLOOM_DIV);
  68                 val = wcscspn_bloom2((size_t)*charset);
  69                 bloom[val / BLOOM_DIV] |= (size_t)1 << (val % BLOOM_DIV);
  70         }
  71         while (*++charset);
  72 }
  73
  74 static inline int
  75 wcsspn_in_bloom(const size_t *bloom, wchar_t ch)
  76 {
  77         size_t val;
  78
  79         val = wcscspn_bloom1((size_t)ch);
  80         if (bloom[val / BLOOM_DIV] & ((size_t)1 << (val % BLOOM_DIV)))
  81                 return 1;
  82         val = wcscspn_bloom2((size_t)ch);
  83         if (bloom[val / BLOOM_DIV] & ((size_t)1 << (val % BLOOM_DIV)))
  84                 return 1;
  85         return 0;
  86 }