1/*
2 * Copyright © 2012 Google, Inc.
3 *
4 * This is part of HarfBuzz, a text shaping library.
5 *
6 * Permission is hereby granted, without written agreement and without
7 * license or royalty fees, to use, copy, modify, and distribute this
8 * software and its documentation for any purpose, provided that the
9 * above copyright notice and the following two paragraphs appear in
10 * all copies of this software.
11 *
12 * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
13 * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
14 * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
15 * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
16 * DAMAGE.
17 *
18 * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
19 * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
20 * FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
21 * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
22 * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
23 *
24 * Google Author(s): Behdad Esfahbod
25 */
26
27#ifndef HB_SET_DIGEST_HH
28#define HB_SET_DIGEST_HH
29
30#include "hb.hh"
31
32/*
33 * The set digests here implement various "filters" that support
34 * "approximate member query". Conceptually these are like Bloom
35 * Filter and Quotient Filter, however, much smaller, faster, and
36 * designed to fit the requirements of our uses for glyph coverage
37 * queries.
38 *
39 * Our filters are highly accurate if the lookup covers fairly local
40 * set of glyphs, but fully flooded and ineffective if coverage is
41 * all over the place.
42 *
43 * The frozen-set can be used instead of a digest, to trade more
44 * memory for 100% accuracy, but in practice, that doesn't look like
45 * an attractive trade-off.
46 */
47
48template <typename mask_t, unsigned int shift>
49struct hb_set_digest_lowest_bits_t
50{
51 static constexpr unsigned mask_bytes = sizeof (mask_t);
52 static constexpr unsigned mask_bits = sizeof (mask_t) * 8;
53 static constexpr unsigned num_bits = 0
54 + (mask_bytes >= 1 ? 3 : 0)
55 + (mask_bytes >= 2 ? 1 : 0)
56 + (mask_bytes >= 4 ? 1 : 0)
57 + (mask_bytes >= 8 ? 1 : 0)
58 + (mask_bytes >= 16? 1 : 0)
59 + 0;
60
61 static_assert ((shift < sizeof (hb_codepoint_t) * 8), "");
62 static_assert ((shift + num_bits <= sizeof (hb_codepoint_t) * 8), "");
63
64 void init () { mask = 0; }
65
66 void add (hb_codepoint_t g) { mask |= mask_for (g); }
67
68 bool add_range (hb_codepoint_t a, hb_codepoint_t b)
69 {
70 if ((b >> shift) - (a >> shift) >= mask_bits - 1)
71 mask = (mask_t) -1;
72 else {
73 mask_t ma = mask_for (a);
74 mask_t mb = mask_for (b);
75 mask |= mb + (mb - ma) - (mb < ma);
76 }
77 return true;
78 }
79
80 template <typename T>
81 void add_array (const T *array, unsigned int count, unsigned int stride=sizeof(T))
82 {
83 for (unsigned int i = 0; i < count; i++)
84 {
85 add (*array);
86 array = (const T *) (stride + (const char *) array);
87 }
88 }
89 template <typename T>
90 bool add_sorted_array (const T *array, unsigned int count, unsigned int stride=sizeof(T))
91 {
92 for (unsigned int i = 0; i < count; i++)
93 {
94 add (*array);
95 array = (const T *) (stride + (const char *) array);
96 }
97 return true;
98 }
99
100 bool may_have (hb_codepoint_t g) const
101 { return !!(mask & mask_for (g)); }
102
103 private:
104
105 static mask_t mask_for (hb_codepoint_t g)
106 { return ((mask_t) 1) << ((g >> shift) & (mask_bits - 1)); }
107 mask_t mask;
108};
109
110template <typename head_t, typename tail_t>
111struct hb_set_digest_combiner_t
112{
113 void init ()
114 {
115 head.init ();
116 tail.init ();
117 }
118
119 void add (hb_codepoint_t g)
120 {
121 head.add (g);
122 tail.add (g);
123 }
124
125 bool add_range (hb_codepoint_t a, hb_codepoint_t b)
126 {
127 head.add_range (a, b);
128 tail.add_range (a, b);
129 return true;
130 }
131 template <typename T>
132 void add_array (const T *array, unsigned int count, unsigned int stride=sizeof(T))
133 {
134 head.add_array (array, count, stride);
135 tail.add_array (array, count, stride);
136 }
137 template <typename T>
138 bool add_sorted_array (const T *array, unsigned int count, unsigned int stride=sizeof(T))
139 {
140 head.add_sorted_array (array, count, stride);
141 tail.add_sorted_array (array, count, stride);
142 return true;
143 }
144
145 bool may_have (hb_codepoint_t g) const
146 {
147 return head.may_have (g) && tail.may_have (g);
148 }
149
150 private:
151 head_t head;
152 tail_t tail;
153};
154
155
156/*
157 * hb_set_digest_t
158 *
159 * This is a combination of digests that performs "best".
160 * There is not much science to this: it's a result of intuition
161 * and testing.
162 */
163typedef hb_set_digest_combiner_t
164<
165 hb_set_digest_lowest_bits_t<unsigned long, 4>,
166 hb_set_digest_combiner_t
167 <
168 hb_set_digest_lowest_bits_t<unsigned long, 0>,
169 hb_set_digest_lowest_bits_t<unsigned long, 9>
170 >
171> hb_set_digest_t;
172
173
174#endif /* HB_SET_DIGEST_HH */
175