1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
|
/*
* Copyright © 2012 Google, Inc.
*
* This is part of HarfBuzz, a text shaping library.
*
* Permission is hereby granted, without written agreement and without
* license or royalty fees, to use, copy, modify, and distribute this
* software and its documentation for any purpose, provided that the
* above copyright notice and the following two paragraphs appear in
* all copies of this software.
*
* IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
* DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
* ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
* IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
* DAMAGE.
*
* THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
* BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
* FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
* ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
* PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
*
* Google Author(s): Behdad Esfahbod
*/
#ifndef HB_SET_DIGEST_HH
#define HB_SET_DIGEST_HH
#include "hb.hh"
/*
* The set digests here implement various "filters" that support
* "approximate member query". Conceptually these are like Bloom
* Filter and Quotient Filter, however, much smaller, faster, and
* designed to fit the requirements of our uses for glyph coverage
* queries.
*
* Our filters are highly accurate if the lookup covers fairly local
* set of glyphs, but fully flooded and ineffective if coverage is
* all over the place.
*
* The frozen-set can be used instead of a digest, to trade more
* memory for 100% accuracy, but in practice, that doesn't look like
* an attractive trade-off.
*/
template <typename mask_t, unsigned int shift>
struct hb_set_digest_lowest_bits_t
{
static constexpr unsigned mask_bytes = sizeof (mask_t);
static constexpr unsigned mask_bits = sizeof (mask_t) * 8;
static constexpr unsigned num_bits = 0
+ (mask_bytes >= 1 ? 3 : 0)
+ (mask_bytes >= 2 ? 1 : 0)
+ (mask_bytes >= 4 ? 1 : 0)
+ (mask_bytes >= 8 ? 1 : 0)
+ (mask_bytes >= 16? 1 : 0)
+ 0;
static_assert ((shift < sizeof (hb_codepoint_t) * 8), "");
static_assert ((shift + num_bits <= sizeof (hb_codepoint_t) * 8), "");
void init () { mask = 0; }
void add (hb_codepoint_t g) { mask |= mask_for (g); }
bool add_range (hb_codepoint_t a, hb_codepoint_t b)
{
if ((b >> shift) - (a >> shift) >= mask_bits - 1)
mask = (mask_t) -1;
else {
mask_t ma = mask_for (a);
mask_t mb = mask_for (b);
mask |= mb + (mb - ma) - (mb < ma);
}
return true;
}
template <typename T>
void add_array (const T *array, unsigned int count, unsigned int stride=sizeof(T))
{
for (unsigned int i = 0; i < count; i++)
{
add (*array);
array = (const T *) (stride + (const char *) array);
}
}
template <typename T>
void add_array (const hb_array_t<const T>& arr) { add_array (&arr, arr.len ()); }
template <typename T>
bool add_sorted_array (const T *array, unsigned int count, unsigned int stride=sizeof(T))
{
for (unsigned int i = 0; i < count; i++)
{
add (*array);
array = (const T *) (stride + (const char *) array);
}
return true;
}
template <typename T>
bool add_sorted_array (const hb_sorted_array_t<const T>& arr) { return add_sorted_array (&arr, arr.len ()); }
bool may_have (hb_codepoint_t g) const
{ return !!(mask & mask_for (g)); }
private:
static mask_t mask_for (hb_codepoint_t g)
{ return ((mask_t) 1) << ((g >> shift) & (mask_bits - 1)); }
mask_t mask;
};
template <typename head_t, typename tail_t>
struct hb_set_digest_combiner_t
{
void init ()
{
head.init ();
tail.init ();
}
void add (hb_codepoint_t g)
{
head.add (g);
tail.add (g);
}
bool add_range (hb_codepoint_t a, hb_codepoint_t b)
{
head.add_range (a, b);
tail.add_range (a, b);
return true;
}
template <typename T>
void add_array (const T *array, unsigned int count, unsigned int stride=sizeof(T))
{
head.add_array (array, count, stride);
tail.add_array (array, count, stride);
}
template <typename T>
void add_array (const hb_array_t<const T>& arr) { add_array (&arr, arr.len ()); }
template <typename T>
bool add_sorted_array (const T *array, unsigned int count, unsigned int stride=sizeof(T))
{
head.add_sorted_array (array, count, stride);
tail.add_sorted_array (array, count, stride);
return true;
}
template <typename T>
bool add_sorted_array (const hb_sorted_array_t<const T>& arr) { return add_sorted_array (&arr, arr.len ()); }
bool may_have (hb_codepoint_t g) const
{
return head.may_have (g) && tail.may_have (g);
}
private:
head_t head;
tail_t tail;
};
/*
* hb_set_digest_t
*
* This is a combination of digests that performs "best".
* There is not much science to this: it's a result of intuition
* and testing.
*/
typedef hb_set_digest_combiner_t
<
hb_set_digest_lowest_bits_t<unsigned long, 4>,
hb_set_digest_combiner_t
<
hb_set_digest_lowest_bits_t<unsigned long, 0>,
hb_set_digest_lowest_bits_t<unsigned long, 9>
>
> hb_set_digest_t;
#endif /* HB_SET_DIGEST_HH */
|