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