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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.
// Package utf8 implements functions and constants to support text encoded in
// UTF-8. It includes functions to translate between runes and UTF-8 byte sequences.
package utf8
// The conditions RuneError==unicode.ReplacementChar and
// MaxRune==unicode.MaxRune are verified in the tests.
// Defining them locally avoids this package depending on package unicode.
// Numbers fundamental to the encoding.
const (
RuneError = '\uFFFD' // the "error" Rune or "Unicode replacement character"
RuneSelf = 0x80 // characters below Runeself are represented as themselves in a single byte.
MaxRune = '\U0010FFFF' // Maximum valid Unicode code point.
UTFMax = 4 // maximum number of bytes of a UTF-8 encoded Unicode character.
)
// Code points in the surrogate range are not valid for UTF-8.
const (
surrogateMin = 0xD800
surrogateMax = 0xDFFF
)
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
// The default lowest and highest continuation byte.
locb = 0x80 // 1000 0000
hicb = 0xBF // 1011 1111
// These names of these constants are chosen to give nice alignment in the
// table below. The first nibble is an index into acceptRanges or F for
// special one-byte cases. The second nibble is the Rune length or the
// Status for the special one-byte case.
xx = 0xF1 // invalid: size 1
as = 0xF0 // ASCII: size 1
s1 = 0x02 // accept 0, size 2
s2 = 0x13 // accept 1, size 3
s3 = 0x03 // accept 0, size 3
s4 = 0x23 // accept 2, size 3
s5 = 0x34 // accept 3, size 4
s6 = 0x04 // accept 0, size 4
s7 = 0x44 // accept 4, size 4
)
// first is information about the first byte in a UTF-8 sequence.
var first = [256]uint8{
// 1 2 3 4 5 6 7 8 9 A B C D E F
as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x00-0x0F
as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x10-0x1F
as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x20-0x2F
as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x30-0x3F
as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x40-0x4F
as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x50-0x5F
as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x60-0x6F
as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x70-0x7F
// 1 2 3 4 5 6 7 8 9 A B C D E F
xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0x80-0x8F
xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0x90-0x9F
xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xA0-0xAF
xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xB0-0xBF
xx, xx, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, // 0xC0-0xCF
s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, // 0xD0-0xDF
s2, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s4, s3, s3, // 0xE0-0xEF
s5, s6, s6, s6, s7, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xF0-0xFF
}
// acceptRange gives the range of valid values for the second byte in a UTF-8
// sequence.
type acceptRange struct {
lo uint8 // lowest value for second byte.
hi uint8 // highest value for second byte.
}
var acceptRanges = [...]acceptRange{
0: {locb, hicb},
1: {0xA0, hicb},
2: {locb, 0x9F},
3: {0x90, hicb},
4: {locb, 0x8F},
}
// 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 {
n := len(p)
if n == 0 {
return false
}
x := first[p[0]]
if n >= int(x&7) {
return true // ASCII, invalid or valid.
}
// Must be short or invalid.
accept := acceptRanges[x>>4]
if n > 1 && (p[1] < accept.lo || accept.hi < p[1]) {
return true
} else if n > 2 && (p[2] < locb || hicb < p[2]) {
return true
}
return false
}
// FullRuneInString is like FullRune but its input is a string.
func FullRuneInString(s string) bool {
n := len(s)
if n == 0 {
return false
}
x := first[s[0]]
if n >= int(x&7) {
return true // ASCII, invalid, or valid.
}
// Must be short or invalid.
accept := acceptRanges[x>>4]
if n > 1 && (s[1] < accept.lo || accept.hi < s[1]) {
return true
} else if n > 2 && (s[2] < locb || hicb < s[2]) {
return true
}
return false
}
// DecodeRune unpacks the first UTF-8 encoding in p and returns the rune and
// its width in bytes. If p is empty it returns (RuneError, 0). Otherwise, if
// the encoding is invalid, it returns (RuneError, 1). Both are impossible
// results for correct, non-empty UTF-8.
//
// An encoding is invalid if it is incorrect UTF-8, encodes a rune that is
// out of range, or is not the shortest possible UTF-8 encoding for the
// value. No other validation is performed.
func DecodeRune(p []byte) (r rune, size int) {
n := len(p)
if n < 1 {
return RuneError, 0
}
p0 := p[0]
x := first[p0]
if x >= as {
// The following code simulates an additional check for x == xx and
// handling the ASCII and invalid cases accordingly. This mask-and-or
// approach prevents an additional branch.
mask := rune(x) << 31 >> 31 // Create 0x0000 or 0xFFFF.
return rune(p[0])&^mask | RuneError&mask, 1
}
sz := x & 7
accept := acceptRanges[x>>4]
if n < int(sz) {
return RuneError, 1
}
b1 := p[1]
if b1 < accept.lo || accept.hi < b1 {
return RuneError, 1
}
if sz == 2 {
return rune(p0&mask2)<<6 | rune(b1&maskx), 2
}
b2 := p[2]
if b2 < locb || hicb < b2 {
return RuneError, 1
}
if sz == 3 {
return rune(p0&mask3)<<12 | rune(b1&maskx)<<6 | rune(b2&maskx), 3
}
b3 := p[3]
if b3 < locb || hicb < b3 {
return RuneError, 1
}
return rune(p0&mask4)<<18 | rune(b1&maskx)<<12 | rune(b2&maskx)<<6 | rune(b3&maskx), 4
}
// DecodeRuneInString is like DecodeRune but its input is a string. If s is
// empty it returns (RuneError, 0). Otherwise, if the encoding is invalid, it
// returns (RuneError, 1). Both are impossible results for correct, non-empty
// UTF-8.
//
// An encoding is invalid if it is incorrect UTF-8, encodes a rune that is
// out of range, or is not the shortest possible UTF-8 encoding for the
// value. No other validation is performed.
func DecodeRuneInString(s string) (r rune, size int) {
n := len(s)
if n < 1 {
return RuneError, 0
}
s0 := s[0]
x := first[s0]
if x >= as {
// The following code simulates an additional check for x == xx and
// handling the ASCII and invalid cases accordingly. This mask-and-or
// approach prevents an additional branch.
mask := rune(x) << 31 >> 31 // Create 0x0000 or 0xFFFF.
return rune(s[0])&^mask | RuneError&mask, 1
}
sz := x & 7
accept := acceptRanges[x>>4]
if n < int(sz) {
return RuneError, 1
}
s1 := s[1]
if s1 < accept.lo || accept.hi < s1 {
return RuneError, 1
}
if sz == 2 {
return rune(s0&mask2)<<6 | rune(s1&maskx), 2
}
s2 := s[2]
if s2 < locb || hicb < s2 {
return RuneError, 1
}
if sz == 3 {
return rune(s0&mask3)<<12 | rune(s1&maskx)<<6 | rune(s2&maskx), 3
}
s3 := s[3]
if s3 < locb || hicb < s3 {
return RuneError, 1
}
return rune(s0&mask4)<<18 | rune(s1&maskx)<<12 | rune(s2&maskx)<<6 | rune(s3&maskx), 4
}
// DecodeLastRune unpacks the last UTF-8 encoding in p and returns the rune and
// its width in bytes. If p is empty it returns (RuneError, 0). Otherwise, if
// the encoding is invalid, it returns (RuneError, 1). Both are impossible
// results for correct, non-empty UTF-8.
//
// An encoding is invalid if it is incorrect UTF-8, encodes a rune that is
// out of range, or is not the shortest possible UTF-8 encoding for the
// value. No other validation is performed.
func DecodeLastRune(p []byte) (r rune, size int) {
end := len(p)
if end == 0 {
return RuneError, 0
}
start := end - 1
r = rune(p[start])
if r < RuneSelf {
return r, 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
}
r, size = DecodeRune(p[start:end])
if start+size != end {
return RuneError, 1
}
return r, size
}
// DecodeLastRuneInString is like DecodeLastRune but its input is a string. If
// s is empty it returns (RuneError, 0). Otherwise, if the encoding is invalid,
// it returns (RuneError, 1). Both are impossible results for correct,
// non-empty UTF-8.
//
// An encoding is invalid if it is incorrect UTF-8, encodes a rune that is
// out of range, or is not the shortest possible UTF-8 encoding for the
// value. No other validation is performed.
func DecodeLastRuneInString(s string) (r rune, size int) {
end := len(s)
if end == 0 {
return RuneError, 0
}
start := end - 1
r = rune(s[start])
if r < RuneSelf {
return r, 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
}
r, size = DecodeRuneInString(s[start:end])
if start+size != end {
return RuneError, 1
}
return r, size
}
// RuneLen returns the number of bytes required to encode the rune.
// It returns -1 if the rune is not a valid value to encode in UTF-8.
func RuneLen(r rune) int {
switch {
case r < 0:
return -1
case r <= rune1Max:
return 1
case r <= rune2Max:
return 2
case surrogateMin <= r && r <= surrogateMax:
return -1
case r <= rune3Max:
return 3
case r <= MaxRune:
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, r rune) int {
// Negative values are erroneous. Making it unsigned addresses the problem.
switch i := uint32(r); {
case i <= rune1Max:
p[0] = byte(r)
return 1
case i <= rune2Max:
_ = p[1] // eliminate bounds checks
p[0] = t2 | byte(r>>6)
p[1] = tx | byte(r)&maskx
return 2
case i > MaxRune, surrogateMin <= i && i <= surrogateMax:
r = RuneError
fallthrough
case i <= rune3Max:
_ = p[2] // eliminate bounds checks
p[0] = t3 | byte(r>>12)
p[1] = tx | byte(r>>6)&maskx
p[2] = tx | byte(r)&maskx
return 3
default:
_ = p[3] // eliminate bounds checks
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 {
np := len(p)
var n int
for i := 0; i < np; {
n++
c := p[i]
if c < RuneSelf {
// ASCII fast path
i++
continue
}
x := first[c]
if x == xx {
i++ // invalid.
continue
}
size := int(x & 7)
if i+size > np {
i++ // Short or invalid.
continue
}
accept := acceptRanges[x>>4]
if c := p[i+1]; c < accept.lo || accept.hi < c {
size = 1
} else if size == 2 {
} else if c := p[i+2]; c < locb || hicb < c {
size = 1
} else if size == 3 {
} else if c := p[i+3]; c < locb || hicb < c {
size = 1
}
i += size
}
return n
}
// RuneCountInString is like RuneCount but its input is a string.
func RuneCountInString(s string) (n int) {
ns := len(s)
for i := 0; i < ns; n++ {
c := s[i]
if c < RuneSelf {
// ASCII fast path
i++
continue
}
x := first[c]
if x == xx {
i++ // invalid.
continue
}
size := int(x & 7)
if i+size > ns {
i++ // Short or invalid.
continue
}
accept := acceptRanges[x>>4]
if c := s[i+1]; c < accept.lo || accept.hi < c {
size = 1
} else if size == 2 {
} else if c := s[i+2]; c < locb || hicb < c {
size = 1
} else if size == 3 {
} else if c := s[i+3]; c < locb || hicb < c {
size = 1
}
i += size
}
return n
}
// RuneStart reports whether the byte could be the first byte of an encoded,
// possibly invalid rune. Second and subsequent bytes always have the top two
// bits set to 10.
func RuneStart(b byte) bool { return b&0xC0 != 0x80 }
// Valid reports whether p consists entirely of valid UTF-8-encoded runes.
func Valid(p []byte) bool {
n := len(p)
for i := 0; i < n; {
pi := p[i]
if pi < RuneSelf {
i++
continue
}
x := first[pi]
if x == xx {
return false // Illegal starter byte.
}
size := int(x & 7)
if i+size > n {
return false // Short or invalid.
}
accept := acceptRanges[x>>4]
if c := p[i+1]; c < accept.lo || accept.hi < c {
return false
} else if size == 2 {
} else if c := p[i+2]; c < locb || hicb < c {
return false
} else if size == 3 {
} else if c := p[i+3]; c < locb || hicb < c {
return false
}
i += size
}
return true
}
// ValidString reports whether s consists entirely of valid UTF-8-encoded runes.
func ValidString(s string) bool {
n := len(s)
for i := 0; i < n; {
si := s[i]
if si < RuneSelf {
i++
continue
}
x := first[si]
if x == xx {
return false // Illegal starter byte.
}
size := int(x & 7)
if i+size > n {
return false // Short or invalid.
}
accept := acceptRanges[x>>4]
if c := s[i+1]; c < accept.lo || accept.hi < c {
return false
} else if size == 2 {
} else if c := s[i+2]; c < locb || hicb < c {
return false
} else if size == 3 {
} else if c := s[i+3]; c < locb || hicb < c {
return false
}
i += size
}
return true
}
// ValidRune reports whether r can be legally encoded as UTF-8.
// Code points that are out of range or a surrogate half are illegal.
func ValidRune(r rune) bool {
switch {
case 0 <= r && r < surrogateMin:
return true
case surrogateMax < r && r <= MaxRune:
return true
}
return false
}