1// Copyright 2016 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package bidi
6
7import "unicode/utf8"
8
9// Properties provides access to BiDi properties of runes.
10type Properties struct {
11 entry uint8
12 last uint8
13}
14
15var trie = newBidiTrie(0)
16
17// TODO: using this for bidirule reduces the running time by about 5%. Consider
18// if this is worth exposing or if we can find a way to speed up the Class
19// method.
20//
21// // CompactClass is like Class, but maps all of the BiDi control classes
22// // (LRO, RLO, LRE, RLE, PDF, LRI, RLI, FSI, PDI) to the class Control.
23// func (p Properties) CompactClass() Class {
24// return Class(p.entry & 0x0F)
25// }
26
27// Class returns the Bidi class for p.
28func (p Properties) Class() Class {
29 c := Class(p.entry & 0x0F)
30 if c == Control {
31 c = controlByteToClass[p.last&0xF]
32 }
33 return c
34}
35
36// IsBracket reports whether the rune is a bracket.
37func (p Properties) IsBracket() bool { return p.entry&0xF0 != 0 }
38
39// IsOpeningBracket reports whether the rune is an opening bracket.
40// IsBracket must return true.
41func (p Properties) IsOpeningBracket() bool { return p.entry&openMask != 0 }
42
43// TODO: find a better API and expose.
44func (p Properties) reverseBracket(r rune) rune {
45 return xorMasks[p.entry>>xorMaskShift] ^ r
46}
47
48var controlByteToClass = [16]Class{
49 0xD: LRO, // U+202D LeftToRightOverride,
50 0xE: RLO, // U+202E RightToLeftOverride,
51 0xA: LRE, // U+202A LeftToRightEmbedding,
52 0xB: RLE, // U+202B RightToLeftEmbedding,
53 0xC: PDF, // U+202C PopDirectionalFormat,
54 0x6: LRI, // U+2066 LeftToRightIsolate,
55 0x7: RLI, // U+2067 RightToLeftIsolate,
56 0x8: FSI, // U+2068 FirstStrongIsolate,
57 0x9: PDI, // U+2069 PopDirectionalIsolate,
58}
59
60// LookupRune returns properties for r.
61func LookupRune(r rune) (p Properties, size int) {
62 var buf [4]byte
63 n := utf8.EncodeRune(buf[:], r)
64 return Lookup(buf[:n])
65}
66
67// TODO: these lookup methods are based on the generated trie code. The returned
68// sizes have slightly different semantics from the generated code, in that it
69// always returns size==1 for an illegal UTF-8 byte (instead of the length
70// of the maximum invalid subsequence). Most Transformers, like unicode/norm,
71// leave invalid UTF-8 untouched, in which case it has performance benefits to
72// do so (without changing the semantics). Bidi requires the semantics used here
73// for the bidirule implementation to be compatible with the Go semantics.
74// They ultimately should perhaps be adopted by all trie implementations, for
75// convenience sake.
76// This unrolled code also boosts performance of the secure/bidirule package by
77// about 30%.
78// So, to remove this code:
79// - add option to trie generator to define return type.
80// - always return 1 byte size for ill-formed UTF-8 runes.
81
82// Lookup returns properties for the first rune in s and the width in bytes of
83// its encoding. The size will be 0 if s does not hold enough bytes to complete
84// the encoding.
85func Lookup(s []byte) (p Properties, sz int) {
86 c0 := s[0]
87 switch {
88 case c0 < 0x80: // is ASCII
89 return Properties{entry: bidiValues[c0]}, 1
90 case c0 < 0xC2:
91 return Properties{}, 1
92 case c0 < 0xE0: // 2-byte UTF-8
93 if len(s) < 2 {
94 return Properties{}, 0
95 }
96 i := bidiIndex[c0]
97 c1 := s[1]
98 if c1 < 0x80 || 0xC0 <= c1 {
99 return Properties{}, 1
100 }
101 return Properties{entry: trie.lookupValue(uint32(i), c1)}, 2
102 case c0 < 0xF0: // 3-byte UTF-8
103 if len(s) < 3 {
104 return Properties{}, 0
105 }
106 i := bidiIndex[c0]
107 c1 := s[1]
108 if c1 < 0x80 || 0xC0 <= c1 {
109 return Properties{}, 1
110 }
111 o := uint32(i)<<6 + uint32(c1)
112 i = bidiIndex[o]
113 c2 := s[2]
114 if c2 < 0x80 || 0xC0 <= c2 {
115 return Properties{}, 1
116 }
117 return Properties{entry: trie.lookupValue(uint32(i), c2), last: c2}, 3
118 case c0 < 0xF8: // 4-byte UTF-8
119 if len(s) < 4 {
120 return Properties{}, 0
121 }
122 i := bidiIndex[c0]
123 c1 := s[1]
124 if c1 < 0x80 || 0xC0 <= c1 {
125 return Properties{}, 1
126 }
127 o := uint32(i)<<6 + uint32(c1)
128 i = bidiIndex[o]
129 c2 := s[2]
130 if c2 < 0x80 || 0xC0 <= c2 {
131 return Properties{}, 1
132 }
133 o = uint32(i)<<6 + uint32(c2)
134 i = bidiIndex[o]
135 c3 := s[3]
136 if c3 < 0x80 || 0xC0 <= c3 {
137 return Properties{}, 1
138 }
139 return Properties{entry: trie.lookupValue(uint32(i), c3)}, 4
140 }
141 // Illegal rune
142 return Properties{}, 1
143}
144
145// LookupString returns properties for the first rune in s and the width in
146// bytes of its encoding. The size will be 0 if s does not hold enough bytes to
147// complete the encoding.
148func LookupString(s string) (p Properties, sz int) {
149 c0 := s[0]
150 switch {
151 case c0 < 0x80: // is ASCII
152 return Properties{entry: bidiValues[c0]}, 1
153 case c0 < 0xC2:
154 return Properties{}, 1
155 case c0 < 0xE0: // 2-byte UTF-8
156 if len(s) < 2 {
157 return Properties{}, 0
158 }
159 i := bidiIndex[c0]
160 c1 := s[1]
161 if c1 < 0x80 || 0xC0 <= c1 {
162 return Properties{}, 1
163 }
164 return Properties{entry: trie.lookupValue(uint32(i), c1)}, 2
165 case c0 < 0xF0: // 3-byte UTF-8
166 if len(s) < 3 {
167 return Properties{}, 0
168 }
169 i := bidiIndex[c0]
170 c1 := s[1]
171 if c1 < 0x80 || 0xC0 <= c1 {
172 return Properties{}, 1
173 }
174 o := uint32(i)<<6 + uint32(c1)
175 i = bidiIndex[o]
176 c2 := s[2]
177 if c2 < 0x80 || 0xC0 <= c2 {
178 return Properties{}, 1
179 }
180 return Properties{entry: trie.lookupValue(uint32(i), c2), last: c2}, 3
181 case c0 < 0xF8: // 4-byte UTF-8
182 if len(s) < 4 {
183 return Properties{}, 0
184 }
185 i := bidiIndex[c0]
186 c1 := s[1]
187 if c1 < 0x80 || 0xC0 <= c1 {
188 return Properties{}, 1
189 }
190 o := uint32(i)<<6 + uint32(c1)
191 i = bidiIndex[o]
192 c2 := s[2]
193 if c2 < 0x80 || 0xC0 <= c2 {
194 return Properties{}, 1
195 }
196 o = uint32(i)<<6 + uint32(c2)
197 i = bidiIndex[o]
198 c3 := s[3]
199 if c3 < 0x80 || 0xC0 <= c3 {
200 return Properties{}, 1
201 }
202 return Properties{entry: trie.lookupValue(uint32(i), c3)}, 4
203 }
204 // Illegal rune
205 return Properties{}, 1
206}