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// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package bidi
import "unicode/utf8"
// Properties provides access to BiDi properties of runes.
type Properties struct {
entry uint8
last uint8
}
var trie = newBidiTrie(0)
// TODO: using this for bidirule reduces the running time by about 5%. Consider
// if this is worth exposing or if we can find a way to speed up the Class
// method.
//
// // CompactClass is like Class, but maps all of the BiDi control classes
// // (LRO, RLO, LRE, RLE, PDF, LRI, RLI, FSI, PDI) to the class Control.
// func (p Properties) CompactClass() Class {
// return Class(p.entry & 0x0F)
// }
// Class returns the Bidi class for p.
func (p Properties) Class() Class {
c := Class(p.entry & 0x0F)
if c == Control {
c = controlByteToClass[p.last&0xF]
}
return c
}
// IsBracket reports whether the rune is a bracket.
func (p Properties) IsBracket() bool { return p.entry&0xF0 != 0 }
// IsOpeningBracket reports whether the rune is an opening bracket.
// IsBracket must return true.
func (p Properties) IsOpeningBracket() bool { return p.entry&openMask != 0 }
// TODO: find a better API and expose.
func (p Properties) reverseBracket(r rune) rune {
return xorMasks[p.entry>>xorMaskShift] ^ r
}
var controlByteToClass = [16]Class{
0xD: LRO, // U+202D LeftToRightOverride,
0xE: RLO, // U+202E RightToLeftOverride,
0xA: LRE, // U+202A LeftToRightEmbedding,
0xB: RLE, // U+202B RightToLeftEmbedding,
0xC: PDF, // U+202C PopDirectionalFormat,
0x6: LRI, // U+2066 LeftToRightIsolate,
0x7: RLI, // U+2067 RightToLeftIsolate,
0x8: FSI, // U+2068 FirstStrongIsolate,
0x9: PDI, // U+2069 PopDirectionalIsolate,
}
// LookupRune returns properties for r.
func LookupRune(r rune) (p Properties, size int) {
var buf [4]byte
n := utf8.EncodeRune(buf[:], r)
return Lookup(buf[:n])
}
// TODO: these lookup methods are based on the generated trie code. The returned
// sizes have slightly different semantics from the generated code, in that it
// always returns size==1 for an illegal UTF-8 byte (instead of the length
// of the maximum invalid subsequence). Most Transformers, like unicode/norm,
// leave invalid UTF-8 untouched, in which case it has performance benefits to
// do so (without changing the semantics). Bidi requires the semantics used here
// for the bidirule implementation to be compatible with the Go semantics.
// They ultimately should perhaps be adopted by all trie implementations, for
// convenience sake.
// This unrolled code also boosts performance of the secure/bidirule package by
// about 30%.
// So, to remove this code:
// - add option to trie generator to define return type.
// - always return 1 byte size for ill-formed UTF-8 runes.
// Lookup returns properties for the first rune in s and the width in bytes of
// its encoding. The size will be 0 if s does not hold enough bytes to complete
// the encoding.
func Lookup(s []byte) (p Properties, sz int) {
c0 := s[0]
switch {
case c0 < 0x80: // is ASCII
return Properties{entry: bidiValues[c0]}, 1
case c0 < 0xC2:
return Properties{}, 1
case c0 < 0xE0: // 2-byte UTF-8
if len(s) < 2 {
return Properties{}, 0
}
i := bidiIndex[c0]
c1 := s[1]
if c1 < 0x80 || 0xC0 <= c1 {
return Properties{}, 1
}
return Properties{entry: trie.lookupValue(uint32(i), c1)}, 2
case c0 < 0xF0: // 3-byte UTF-8
if len(s) < 3 {
return Properties{}, 0
}
i := bidiIndex[c0]
c1 := s[1]
if c1 < 0x80 || 0xC0 <= c1 {
return Properties{}, 1
}
o := uint32(i)<<6 + uint32(c1)
i = bidiIndex[o]
c2 := s[2]
if c2 < 0x80 || 0xC0 <= c2 {
return Properties{}, 1
}
return Properties{entry: trie.lookupValue(uint32(i), c2), last: c2}, 3
case c0 < 0xF8: // 4-byte UTF-8
if len(s) < 4 {
return Properties{}, 0
}
i := bidiIndex[c0]
c1 := s[1]
if c1 < 0x80 || 0xC0 <= c1 {
return Properties{}, 1
}
o := uint32(i)<<6 + uint32(c1)
i = bidiIndex[o]
c2 := s[2]
if c2 < 0x80 || 0xC0 <= c2 {
return Properties{}, 1
}
o = uint32(i)<<6 + uint32(c2)
i = bidiIndex[o]
c3 := s[3]
if c3 < 0x80 || 0xC0 <= c3 {
return Properties{}, 1
}
return Properties{entry: trie.lookupValue(uint32(i), c3)}, 4
}
// Illegal rune
return Properties{}, 1
}
// LookupString returns properties for the first rune in s and the width in
// bytes of its encoding. The size will be 0 if s does not hold enough bytes to
// complete the encoding.
func LookupString(s string) (p Properties, sz int) {
c0 := s[0]
switch {
case c0 < 0x80: // is ASCII
return Properties{entry: bidiValues[c0]}, 1
case c0 < 0xC2:
return Properties{}, 1
case c0 < 0xE0: // 2-byte UTF-8
if len(s) < 2 {
return Properties{}, 0
}
i := bidiIndex[c0]
c1 := s[1]
if c1 < 0x80 || 0xC0 <= c1 {
return Properties{}, 1
}
return Properties{entry: trie.lookupValue(uint32(i), c1)}, 2
case c0 < 0xF0: // 3-byte UTF-8
if len(s) < 3 {
return Properties{}, 0
}
i := bidiIndex[c0]
c1 := s[1]
if c1 < 0x80 || 0xC0 <= c1 {
return Properties{}, 1
}
o := uint32(i)<<6 + uint32(c1)
i = bidiIndex[o]
c2 := s[2]
if c2 < 0x80 || 0xC0 <= c2 {
return Properties{}, 1
}
return Properties{entry: trie.lookupValue(uint32(i), c2), last: c2}, 3
case c0 < 0xF8: // 4-byte UTF-8
if len(s) < 4 {
return Properties{}, 0
}
i := bidiIndex[c0]
c1 := s[1]
if c1 < 0x80 || 0xC0 <= c1 {
return Properties{}, 1
}
o := uint32(i)<<6 + uint32(c1)
i = bidiIndex[o]
c2 := s[2]
if c2 < 0x80 || 0xC0 <= c2 {
return Properties{}, 1
}
o = uint32(i)<<6 + uint32(c2)
i = bidiIndex[o]
c3 := s[3]
if c3 < 0x80 || 0xC0 <= c3 {
return Properties{}, 1
}
return Properties{entry: trie.lookupValue(uint32(i), c3)}, 4
}
// Illegal rune
return Properties{}, 1
}
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