// Copyright 2010 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 utf16 implements encoding and decoding of UTF-16 sequences. package utf16 // The conditions replacementChar==unicode.ReplacementChar and // maxRune==unicode.MaxRune are verified in the tests. // Defining them locally avoids this package depending on package unicode. const ( replacementChar = '\uFFFD' // Unicode replacement character maxRune = '\U0010FFFF' // Maximum valid Unicode code point. ) const ( // 0xd800-0xdc00 encodes the high 10 bits of a pair. // 0xdc00-0xe000 encodes the low 10 bits of a pair. // the value is those 20 bits plus 0x10000. surr1 = 0xd800 surr2 = 0xdc00 surr3 = 0xe000 surrSelf = 0x10000 ) // IsSurrogate reports whether the specified Unicode code point // can appear in a surrogate pair. func IsSurrogate(r rune) bool { return surr1 <= r && r < surr3 } // DecodeRune returns the UTF-16 decoding of a surrogate pair. // If the pair is not a valid UTF-16 surrogate pair, DecodeRune returns // the Unicode replacement code point U+FFFD. func DecodeRune(r1, r2 rune) rune { if surr1 <= r1 && r1 < surr2 && surr2 <= r2 && r2 < surr3 { return (r1-surr1)<<10 | (r2 - surr2) + surrSelf } return replacementChar } // EncodeRune returns the UTF-16 surrogate pair r1, r2 for the given rune. // If the rune is not a valid Unicode code point or does not need encoding, // EncodeRune returns U+FFFD, U+FFFD. func EncodeRune(r rune) (r1, r2 rune) { if r < surrSelf || r > maxRune { return replacementChar, replacementChar } r -= surrSelf return surr1 + (r>>10)&0x3ff, surr2 + r&0x3ff } // RuneLen returns the number of 16-bit words in the UTF-16 encoding of the rune. // It returns -1 if the rune is not a valid value to encode in UTF-16. func RuneLen(r rune) int { switch { case 0 <= r && r < surr1, surr3 <= r && r < surrSelf: return 1 case surrSelf <= r && r <= maxRune: return 2 default: return -1 } } // Encode returns the UTF-16 encoding of the Unicode code point sequence s. func Encode(s []rune) []uint16 { n := len(s) for _, v := range s { if v >= surrSelf { n++ } } a := make([]uint16, n) n = 0 for _, v := range s { switch RuneLen(v) { case 1: // normal rune a[n] = uint16(v) n++ case 2: // needs surrogate sequence r1, r2 := EncodeRune(v) a[n] = uint16(r1) a[n+1] = uint16(r2) n += 2 default: a[n] = uint16(replacementChar) n++ } } return a[:n] } // AppendRune appends the UTF-16 encoding of the Unicode code point r // to the end of p and returns the extended buffer. If the rune is not // a valid Unicode code point, it appends the encoding of U+FFFD. func AppendRune(a []uint16, r rune) []uint16 { // This function is inlineable for fast handling of ASCII. switch { case 0 <= r && r < surr1, surr3 <= r && r < surrSelf: // normal rune return append(a, uint16(r)) case surrSelf <= r && r <= maxRune: // needs surrogate sequence r1, r2 := EncodeRune(r) return append(a, uint16(r1), uint16(r2)) } return append(a, replacementChar) } // Decode returns the Unicode code point sequence represented // by the UTF-16 encoding s. func Decode(s []uint16) []rune { // Preallocate capacity to hold up to 64 runes. // Decode inlines, so the allocation can live on the stack. buf := make([]rune, 0, 64) return decode(s, buf) } // decode appends to buf the Unicode code point sequence represented // by the UTF-16 encoding s and return the extended buffer. func decode(s []uint16, buf []rune) []rune { for i := 0; i < len(s); i++ { var ar rune switch r := s[i]; { case r < surr1, surr3 <= r: // normal rune ar = rune(r) case surr1 <= r && r < surr2 && i+1 < len(s) && surr2 <= s[i+1] && s[i+1] < surr3: // valid surrogate sequence ar = DecodeRune(rune(r), rune(s[i+1])) i++ default: // invalid surrogate sequence ar = replacementChar } buf = append(buf, ar) } return buf }