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1 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #include "kern.h"
6 
7 // kern - Kerning
8 // http://www.microsoft.com/opentype/otspec/kern.htm
9 
10 #define DROP_THIS_TABLE \
11   do { delete file->kern; file->kern = 0; } while (0)
12 
13 namespace ots {
14 
ots_kern_parse(OpenTypeFile * file,const uint8_t * data,size_t length)15 bool ots_kern_parse(OpenTypeFile *file, const uint8_t *data, size_t length) {
16   Buffer table(data, length);
17 
18   OpenTypeKERN *kern = new OpenTypeKERN;
19   file->kern = kern;
20 
21   uint16_t num_tables = 0;
22   if (!table.ReadU16(&kern->version) ||
23       !table.ReadU16(&num_tables)) {
24     return OTS_FAILURE();
25   }
26 
27   if (kern->version > 0) {
28     DROP_THIS_TABLE;
29     return true;
30   }
31 
32   if (num_tables == 0) {
33     OTS_WARNING("num_tables is zero");
34     DROP_THIS_TABLE;
35     return true;
36   }
37 
38   kern->subtables.reserve(num_tables);
39   for (unsigned i = 0; i < num_tables; ++i) {
40     OpenTypeKERNFormat0 subtable;
41     uint16_t sub_length = 0;
42 
43     if (!table.ReadU16(&subtable.version) ||
44         !table.ReadU16(&sub_length)) {
45       return OTS_FAILURE();
46     }
47 
48     if (subtable.version > 0) {
49       OTS_WARNING("Bad subtable version: %d", subtable.version);
50       continue;
51     }
52 
53     const size_t current_offset = table.offset();
54     if (current_offset - 4 + sub_length > length) {
55       return OTS_FAILURE();
56     }
57 
58     if (!table.ReadU16(&subtable.coverage)) {
59       return OTS_FAILURE();
60     }
61 
62     if (!(subtable.coverage & 0x1)) {
63       OTS_WARNING(
64           "We don't support vertical data as the renderer doesn't support it.");
65       continue;
66     }
67     if (subtable.coverage & 0xF0) {
68       OTS_WARNING("Reserved fields should zero-filled.");
69       DROP_THIS_TABLE;
70       return true;
71     }
72     const uint32_t format = (subtable.coverage & 0xFF00) >> 8;
73     if (format != 0) {
74       OTS_WARNING("Format %d is not supported.", format);
75       continue;
76     }
77 
78     // Parse the format 0 field.
79     uint16_t num_pairs = 0;
80     if (!table.ReadU16(&num_pairs) ||
81         !table.ReadU16(&subtable.search_range) ||
82         !table.ReadU16(&subtable.entry_selector) ||
83         !table.ReadU16(&subtable.range_shift)) {
84       return OTS_FAILURE();
85     }
86 
87     if (!num_pairs) {
88       OTS_WARNING("Zero length subtable is found.");
89       DROP_THIS_TABLE;
90       return true;
91     }
92 
93     // Sanity checks for search_range, entry_selector, and range_shift. See the
94     // comment in ots.cc for details.
95     const size_t kFormat0PairSize = 6;  // left, right, and value. 2 bytes each.
96     if (num_pairs > (65536 / kFormat0PairSize)) {
97       // Some fonts (e.g. calibri.ttf, pykes_peak_zero.ttf) have pairs >= 10923.
98       OTS_WARNING("Too large subtable.");
99       DROP_THIS_TABLE;
100       return true;
101     }
102     unsigned max_pow2 = 0;
103     while (1u << (max_pow2 + 1) <= num_pairs) {
104       ++max_pow2;
105     }
106     const uint16_t expected_search_range = (1u << max_pow2) * kFormat0PairSize;
107     if (subtable.search_range != expected_search_range) {
108       OTS_WARNING("bad search range");
109       subtable.search_range = expected_search_range;
110     }
111     if (subtable.entry_selector != max_pow2) {
112       return OTS_FAILURE();
113     }
114     const uint32_t expected_range_shift
115         = kFormat0PairSize * num_pairs - subtable.search_range;
116     if (subtable.range_shift != expected_range_shift) {
117       OTS_WARNING("bad range shift");
118       subtable.range_shift = expected_range_shift;
119     }
120 
121     // Read kerning pairs.
122     subtable.pairs.reserve(num_pairs);
123     uint32_t last_pair = 0;
124     for (unsigned j = 0; j < num_pairs; ++j) {
125       OpenTypeKERNFormat0Pair kerning_pair;
126       if (!table.ReadU16(&kerning_pair.left) ||
127           !table.ReadU16(&kerning_pair.right) ||
128           !table.ReadS16(&kerning_pair.value)) {
129         return OTS_FAILURE();
130       }
131       const uint32_t current_pair
132           = (kerning_pair.left << 16) + kerning_pair.right;
133       if (j != 0 && current_pair <= last_pair) {
134         OTS_WARNING("Kerning pairs are not sorted.");
135         // Many free fonts don't follow this rule, so we don't call OTS_FAILURE
136         // in order to support these fonts.
137         DROP_THIS_TABLE;
138         return true;
139       }
140       last_pair = current_pair;
141       subtable.pairs.push_back(kerning_pair);
142     }
143 
144     kern->subtables.push_back(subtable);
145   }
146 
147   if (!kern->subtables.size()) {
148     OTS_WARNING("All subtables are removed.");
149     DROP_THIS_TABLE;
150     return true;
151   }
152 
153   return true;
154 }
155 
ots_kern_should_serialise(OpenTypeFile * file)156 bool ots_kern_should_serialise(OpenTypeFile *file) {
157   if (!file->glyf) return false;  // this table is not for CFF fonts.
158   return file->kern != NULL;
159 }
160 
ots_kern_serialise(OTSStream * out,OpenTypeFile * file)161 bool ots_kern_serialise(OTSStream *out, OpenTypeFile *file) {
162   const OpenTypeKERN *kern = file->kern;
163 
164   if (!out->WriteU16(kern->version) ||
165       !out->WriteU16(kern->subtables.size())) {
166     return OTS_FAILURE();
167   }
168 
169   for (unsigned i = 0; i < kern->subtables.size(); ++i) {
170     const uint16_t length = 14 + (6 * kern->subtables[i].pairs.size());
171     if (!out->WriteU16(kern->subtables[i].version) ||
172         !out->WriteU16(length) ||
173         !out->WriteU16(kern->subtables[i].coverage) ||
174         !out->WriteU16(kern->subtables[i].pairs.size()) ||
175         !out->WriteU16(kern->subtables[i].search_range) ||
176         !out->WriteU16(kern->subtables[i].entry_selector) ||
177         !out->WriteU16(kern->subtables[i].range_shift)) {
178       return OTS_FAILURE();
179     }
180     for (unsigned j = 0; j < kern->subtables[i].pairs.size(); ++j) {
181       if (!out->WriteU16(kern->subtables[i].pairs[j].left) ||
182           !out->WriteU16(kern->subtables[i].pairs[j].right) ||
183           !out->WriteS16(kern->subtables[i].pairs[j].value)) {
184         return OTS_FAILURE();
185       }
186     }
187   }
188 
189   return true;
190 }
191 
ots_kern_free(OpenTypeFile * file)192 void ots_kern_free(OpenTypeFile *file) {
193   delete file->kern;
194 }
195 
196 }  // namespace ots
197