Naveen Sampath | 04696f7 | 2022-06-13 15:19:14 +0530 | [diff] [blame] | 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 | |
| 5 | package bidi |
| 6 | |
| 7 | import "unicode/utf8" |
| 8 | |
| 9 | // Properties provides access to BiDi properties of runes. |
| 10 | type Properties struct { |
| 11 | entry uint8 |
| 12 | last uint8 |
| 13 | } |
| 14 | |
| 15 | var 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. |
| 28 | func (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. |
| 37 | func (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. |
| 41 | func (p Properties) IsOpeningBracket() bool { return p.entry&openMask != 0 } |
| 42 | |
| 43 | // TODO: find a better API and expose. |
| 44 | func (p Properties) reverseBracket(r rune) rune { |
| 45 | return xorMasks[p.entry>>xorMaskShift] ^ r |
| 46 | } |
| 47 | |
| 48 | var 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. |
| 61 | func 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. |
| 85 | func 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. |
| 148 | func 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 | } |