// Copyright 2010 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package utf16 implements encoding and decoding of UTF-16 sequences.
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package utf16
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// The conditions replacementChar==unicode.ReplacementChar and
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// maxRune==unicode.MaxRune are verified in the tests.
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// Defining them locally avoids this package depending on package unicode.
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const (
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replacementChar = '\uFFFD' // Unicode replacement character
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maxRune = '\U0010FFFF' // Maximum valid Unicode code point.
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)
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const (
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// 0xd800-0xdc00 encodes the high 10 bits of a pair.
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// 0xdc00-0xe000 encodes the low 10 bits of a pair.
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// the value is those 20 bits plus 0x10000.
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surr1 = 0xd800
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surr2 = 0xdc00
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surr3 = 0xe000
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surrSelf = 0x10000
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)
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// IsSurrogate reports whether the specified Unicode code point
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// can appear in a surrogate pair.
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func IsSurrogate(r rune) bool {
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return surr1 <= r && r < surr3
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}
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// DecodeRune returns the UTF-16 decoding of a surrogate pair.
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// If the pair is not a valid UTF-16 surrogate pair, DecodeRune returns
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// the Unicode replacement code point U+FFFD.
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func DecodeRune(r1, r2 rune) rune {
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if surr1 <= r1 && r1 < surr2 && surr2 <= r2 && r2 < surr3 {
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return (r1-surr1)<<10 | (r2 - surr2) + surrSelf
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}
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return replacementChar
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}
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// EncodeRune returns the UTF-16 surrogate pair r1, r2 for the given rune.
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// If the rune is not a valid Unicode code point or does not need encoding,
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// EncodeRune returns U+FFFD, U+FFFD.
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func EncodeRune(r rune) (r1, r2 rune) {
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if r < surrSelf || r > maxRune {
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return replacementChar, replacementChar
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}
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r -= surrSelf
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return surr1 + (r>>10)&0x3ff, surr2 + r&0x3ff
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}
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// Encode returns the UTF-16 encoding of the Unicode code point sequence s.
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func Encode(s []rune) []uint16 {
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n := len(s)
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for _, v := range s {
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if v >= surrSelf {
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n++
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}
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}
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a := make([]uint16, n)
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n = 0
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for _, v := range s {
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switch {
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case 0 <= v && v < surr1, surr3 <= v && v < surrSelf:
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// normal rune
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a[n] = uint16(v)
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n++
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case surrSelf <= v && v <= maxRune:
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// needs surrogate sequence
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r1, r2 := EncodeRune(v)
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a[n] = uint16(r1)
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a[n+1] = uint16(r2)
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n += 2
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default:
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a[n] = uint16(replacementChar)
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n++
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}
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}
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return a[:n]
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}
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// Decode returns the Unicode code point sequence represented
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// by the UTF-16 encoding s.
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func Decode(s []uint16) []rune {
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a := make([]rune, len(s))
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n := 0
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for i := 0; i < len(s); i++ {
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switch r := s[i]; {
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case r < surr1, surr3 <= r:
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// normal rune
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a[n] = rune(r)
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case surr1 <= r && r < surr2 && i+1 < len(s) &&
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surr2 <= s[i+1] && s[i+1] < surr3:
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// valid surrogate sequence
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a[n] = DecodeRune(rune(r), rune(s[i+1]))
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i++
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default:
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// invalid surrogate sequence
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a[n] = replacementChar
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}
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n++
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}
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return a[:n]
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}
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