codekingpro/portable-devtools

1// Copyright 2010 The Go Authors. All rights reserved.2// Use of this source code is governed by a BSD-style3// license that can be found in the LICENSE file.4 5// Package utf16 implements encoding and decoding of UTF-16 sequences.6package utf167 8// The conditions replacementChar==unicode.ReplacementChar and9// maxRune==unicode.MaxRune are verified in the tests.10// Defining them locally avoids this package depending on package unicode.11 12const (13	replacementChar = '\uFFFD'     // Unicode replacement character14	maxRune         = '\U0010FFFF' // Maximum valid Unicode code point.15)16 17const (18	// 0xd800-0xdc00 encodes the high 10 bits of a pair.19	// 0xdc00-0xe000 encodes the low 10 bits of a pair.20	// the value is those 20 bits plus 0x10000.21	surr1 = 0xd80022	surr2 = 0xdc0023	surr3 = 0xe00024 25	surrSelf = 0x1000026)27 28// IsSurrogate reports whether the specified Unicode code point29// can appear in a surrogate pair.30func IsSurrogate(r rune) bool {31	return surr1 <= r && r < surr332}33 34// DecodeRune returns the UTF-16 decoding of a surrogate pair.35// If the pair is not a valid UTF-16 surrogate pair, DecodeRune returns36// the Unicode replacement code point U+FFFD.37func DecodeRune(r1, r2 rune) rune {38	if surr1 <= r1 && r1 < surr2 && surr2 <= r2 && r2 < surr3 {39		return (r1-surr1)<<10 | (r2 - surr2) + surrSelf40	}41	return replacementChar42}43 44// EncodeRune returns the UTF-16 surrogate pair r1, r2 for the given rune.45// If the rune is not a valid Unicode code point or does not need encoding,46// EncodeRune returns U+FFFD, U+FFFD.47func EncodeRune(r rune) (r1, r2 rune) {48	if r < surrSelf || r > maxRune {49		return replacementChar, replacementChar50	}51	r -= surrSelf52	return surr1 + (r>>10)&0x3ff, surr2 + r&0x3ff53}54 55// RuneLen returns the number of 16-bit words in the UTF-16 encoding of the rune.56// It returns -1 if the rune is not a valid value to encode in UTF-16.57func RuneLen(r rune) int {58	switch {59	case 0 <= r && r < surr1, surr3 <= r && r < surrSelf:60		return 161	case surrSelf <= r && r <= maxRune:62		return 263	default:64		return -165	}66}67 68// Encode returns the UTF-16 encoding of the Unicode code point sequence s.69func Encode(s []rune) []uint16 {70	n := len(s)71	for _, v := range s {72		if v >= surrSelf {73			n++74		}75	}76 77	a := make([]uint16, n)78	n = 079	for _, v := range s {80		switch RuneLen(v) {81		case 1: // normal rune82			a[n] = uint16(v)83			n++84		case 2: // needs surrogate sequence85			r1, r2 := EncodeRune(v)86			a[n] = uint16(r1)87			a[n+1] = uint16(r2)88			n += 289		default:90			a[n] = uint16(replacementChar)91			n++92		}93	}94	return a[:n]95}96 97// AppendRune appends the UTF-16 encoding of the Unicode code point r98// to the end of p and returns the extended buffer. If the rune is not99// a valid Unicode code point, it appends the encoding of U+FFFD.100func AppendRune(a []uint16, r rune) []uint16 {101	// This function is inlineable for fast handling of ASCII.102	switch {103	case 0 <= r && r < surr1, surr3 <= r && r < surrSelf:104		// normal rune105		return append(a, uint16(r))106	case surrSelf <= r && r <= maxRune:107		// needs surrogate sequence108		r1, r2 := EncodeRune(r)109		return append(a, uint16(r1), uint16(r2))110	}111	return append(a, replacementChar)112}113 114// Decode returns the Unicode code point sequence represented115// by the UTF-16 encoding s.116func Decode(s []uint16) []rune {117	// Preallocate capacity to hold up to 64 runes.118	// Decode inlines, so the allocation can live on the stack.119	buf := make([]rune, 0, 64)120	return decode(s, buf)121}122 123// decode appends to buf the Unicode code point sequence represented124// by the UTF-16 encoding s and return the extended buffer.125func decode(s []uint16, buf []rune) []rune {126	for i := 0; i < len(s); i++ {127		var ar rune128		switch r := s[i]; {129		case r < surr1, surr3 <= r:130			// normal rune131			ar = rune(r)132		case surr1 <= r && r < surr2 && i+1 < len(s) &&133			surr2 <= s[i+1] && s[i+1] < surr3:134			// valid surrogate sequence135			ar = DecodeRune(rune(r), rune(s[i+1]))136			i++137		default:138			// invalid surrogate sequence139			ar = replacementChar140		}141		buf = append(buf, ar)142	}143	return buf144}145