357 lines
7.5 KiB
Go
357 lines
7.5 KiB
Go
// Copyright 2009 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 utf8 implements functions and constants to support text encoded in
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// UTF-8. This package calls a Unicode character a rune for brevity.
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package utf8
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import "unicode" // only needed for a couple of constants
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// Numbers fundamental to the encoding.
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const (
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RuneError = unicode.ReplacementChar // the "error" Rune or "replacement character".
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RuneSelf = 0x80 // characters below Runeself are represented as themselves in a single byte.
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UTFMax = 4 // maximum number of bytes of a UTF-8 encoded Unicode character.
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)
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const (
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_T1 = 0x00 // 0000 0000
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_Tx = 0x80 // 1000 0000
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_T2 = 0xC0 // 1100 0000
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_T3 = 0xE0 // 1110 0000
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_T4 = 0xF0 // 1111 0000
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_T5 = 0xF8 // 1111 1000
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_Maskx = 0x3F // 0011 1111
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_Mask2 = 0x1F // 0001 1111
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_Mask3 = 0x0F // 0000 1111
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_Mask4 = 0x07 // 0000 0111
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_Rune1Max = 1<<7 - 1
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_Rune2Max = 1<<11 - 1
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_Rune3Max = 1<<16 - 1
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_Rune4Max = 1<<21 - 1
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)
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func decodeRuneInternal(p []byte) (rune, size int, short bool) {
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n := len(p)
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if n < 1 {
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return RuneError, 0, true
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}
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c0 := p[0]
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// 1-byte, 7-bit sequence?
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if c0 < _Tx {
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return int(c0), 1, false
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}
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// unexpected continuation byte?
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if c0 < _T2 {
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return RuneError, 1, false
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}
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// need first continuation byte
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if n < 2 {
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return RuneError, 1, true
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}
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c1 := p[1]
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if c1 < _Tx || _T2 <= c1 {
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return RuneError, 1, false
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}
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// 2-byte, 11-bit sequence?
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if c0 < _T3 {
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rune = int(c0&_Mask2)<<6 | int(c1&_Maskx)
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if rune <= _Rune1Max {
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return RuneError, 1, false
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}
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return rune, 2, false
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}
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// need second continuation byte
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if n < 3 {
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return RuneError, 1, true
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}
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c2 := p[2]
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if c2 < _Tx || _T2 <= c2 {
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return RuneError, 1, false
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}
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// 3-byte, 16-bit sequence?
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if c0 < _T4 {
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rune = int(c0&_Mask3)<<12 | int(c1&_Maskx)<<6 | int(c2&_Maskx)
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if rune <= _Rune2Max {
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return RuneError, 1, false
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}
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return rune, 3, false
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}
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// need third continuation byte
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if n < 4 {
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return RuneError, 1, true
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}
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c3 := p[3]
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if c3 < _Tx || _T2 <= c3 {
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return RuneError, 1, false
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}
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// 4-byte, 21-bit sequence?
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if c0 < _T5 {
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rune = int(c0&_Mask4)<<18 | int(c1&_Maskx)<<12 | int(c2&_Maskx)<<6 | int(c3&_Maskx)
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if rune <= _Rune3Max {
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return RuneError, 1, false
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}
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return rune, 4, false
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}
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// error
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return RuneError, 1, false
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}
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func decodeRuneInStringInternal(s string) (rune, size int, short bool) {
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n := len(s)
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if n < 1 {
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return RuneError, 0, true
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}
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c0 := s[0]
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// 1-byte, 7-bit sequence?
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if c0 < _Tx {
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return int(c0), 1, false
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}
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// unexpected continuation byte?
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if c0 < _T2 {
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return RuneError, 1, false
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}
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// need first continuation byte
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if n < 2 {
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return RuneError, 1, true
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}
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c1 := s[1]
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if c1 < _Tx || _T2 <= c1 {
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return RuneError, 1, false
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}
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// 2-byte, 11-bit sequence?
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if c0 < _T3 {
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rune = int(c0&_Mask2)<<6 | int(c1&_Maskx)
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if rune <= _Rune1Max {
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return RuneError, 1, false
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}
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return rune, 2, false
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}
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// need second continuation byte
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if n < 3 {
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return RuneError, 1, true
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}
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c2 := s[2]
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if c2 < _Tx || _T2 <= c2 {
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return RuneError, 1, false
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}
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// 3-byte, 16-bit sequence?
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if c0 < _T4 {
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rune = int(c0&_Mask3)<<12 | int(c1&_Maskx)<<6 | int(c2&_Maskx)
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if rune <= _Rune2Max {
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return RuneError, 1, false
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}
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return rune, 3, false
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}
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// need third continuation byte
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if n < 4 {
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return RuneError, 1, true
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}
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c3 := s[3]
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if c3 < _Tx || _T2 <= c3 {
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return RuneError, 1, false
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}
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// 4-byte, 21-bit sequence?
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if c0 < _T5 {
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rune = int(c0&_Mask4)<<18 | int(c1&_Maskx)<<12 | int(c2&_Maskx)<<6 | int(c3&_Maskx)
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if rune <= _Rune3Max {
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return RuneError, 1, false
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}
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return rune, 4, false
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}
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// error
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return RuneError, 1, false
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}
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// FullRune reports whether the bytes in p begin with a full UTF-8 encoding of a rune.
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// An invalid encoding is considered a full Rune since it will convert as a width-1 error rune.
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func FullRune(p []byte) bool {
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_, _, short := decodeRuneInternal(p)
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return !short
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}
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// FullRuneInString is like FullRune but its input is a string.
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func FullRuneInString(s string) bool {
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_, _, short := decodeRuneInStringInternal(s)
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return !short
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}
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// DecodeRune unpacks the first UTF-8 encoding in p and returns the rune and its width in bytes.
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func DecodeRune(p []byte) (rune, size int) {
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rune, size, _ = decodeRuneInternal(p)
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return
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}
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// DecodeRuneInString is like DecodeRune but its input is a string.
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func DecodeRuneInString(s string) (rune, size int) {
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rune, size, _ = decodeRuneInStringInternal(s)
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return
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}
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// DecodeLastRune unpacks the last UTF-8 encoding in p
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// and returns the rune and its width in bytes.
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func DecodeLastRune(p []byte) (rune, size int) {
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end := len(p)
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if end == 0 {
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return RuneError, 0
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}
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start := end - 1
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rune = int(p[start])
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if rune < RuneSelf {
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return rune, 1
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}
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// guard against O(n^2) behavior when traversing
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// backwards through strings with long sequences of
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// invalid UTF-8.
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lim := end - UTFMax
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if lim < 0 {
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lim = 0
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}
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for start--; start >= lim; start-- {
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if RuneStart(p[start]) {
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break
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}
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}
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if start < 0 {
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start = 0
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}
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rune, size = DecodeRune(p[start:end])
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if start+size != end {
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return RuneError, 1
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}
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return rune, size
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}
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// DecodeLastRuneInString is like DecodeLastRune but its input is a string.
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func DecodeLastRuneInString(s string) (rune, size int) {
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end := len(s)
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if end == 0 {
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return RuneError, 0
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}
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start := end - 1
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rune = int(s[start])
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if rune < RuneSelf {
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return rune, 1
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}
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// guard against O(n^2) behavior when traversing
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// backwards through strings with long sequences of
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// invalid UTF-8.
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lim := end - UTFMax
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if lim < 0 {
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lim = 0
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}
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for start--; start >= lim; start-- {
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if RuneStart(s[start]) {
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break
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}
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}
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if start < 0 {
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start = 0
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}
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rune, size = DecodeRuneInString(s[start:end])
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if start+size != end {
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return RuneError, 1
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}
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return rune, size
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}
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// RuneLen returns the number of bytes required to encode the rune.
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func RuneLen(rune int) int {
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switch {
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case rune <= _Rune1Max:
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return 1
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case rune <= _Rune2Max:
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return 2
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case rune <= _Rune3Max:
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return 3
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case rune <= _Rune4Max:
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return 4
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}
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return -1
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}
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// EncodeRune writes into p (which must be large enough) the UTF-8 encoding of the rune.
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// It returns the number of bytes written.
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func EncodeRune(p []byte, rune int) int {
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// Negative values are erroneous. Making it unsigned addresses the problem.
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r := uint(rune)
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if r <= _Rune1Max {
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p[0] = byte(r)
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return 1
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}
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if r <= _Rune2Max {
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p[0] = _T2 | byte(r>>6)
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p[1] = _Tx | byte(r)&_Maskx
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return 2
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}
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if r > unicode.MaxRune {
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r = RuneError
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}
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if r <= _Rune3Max {
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p[0] = _T3 | byte(r>>12)
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p[1] = _Tx | byte(r>>6)&_Maskx
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p[2] = _Tx | byte(r)&_Maskx
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return 3
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}
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p[0] = _T4 | byte(r>>18)
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p[1] = _Tx | byte(r>>12)&_Maskx
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p[2] = _Tx | byte(r>>6)&_Maskx
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p[3] = _Tx | byte(r)&_Maskx
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return 4
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}
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// RuneCount returns the number of runes in p. Erroneous and short
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// encodings are treated as single runes of width 1 byte.
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func RuneCount(p []byte) int {
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i := 0
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var n int
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for n = 0; i < len(p); n++ {
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if p[i] < RuneSelf {
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i++
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} else {
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_, size := DecodeRune(p[i:])
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i += size
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}
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}
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return n
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}
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// RuneCountInString is like RuneCount but its input is a string.
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func RuneCountInString(s string) (n int) {
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for _ = range s {
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n++
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}
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return
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}
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// RuneStart reports whether the byte could be the first byte of
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// an encoded rune. Second and subsequent bytes always have the top
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// two bits set to 10.
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func RuneStart(b byte) bool { return b&0xC0 != 0x80 }
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