golang utf8 代码
文件路径：/src/unicode/utf8/utf8.go
/ 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.
/ See https://en.wikipedia.org/wiki/UTF-8
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 = 0b00000000
tx = 0b10000000
t2 = 0b11000000
t3 = 0b11100000
t4 = 0b11110000
t5 = 0b11111000
maskx = 0b00111111
mask2 = 0b00011111
mask3 = 0b00001111
mask4 = 0b00000111
rune1Max = 1<<7 - 1
rune2Max = 1<<11 - 1
rune3Max = 1<<16 - 1
/ The default lowest and highest continuation byte.
locb = 0b10000000
hicb = 0b10111111
/ 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.
}
/ acceptRanges has size 16 to avoid bounds checks in the code that uses it.
var acceptRanges = [16]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 := int(x & 7)
accept := acceptRanges[x>>4]
if n < sz {
return RuneError, 1
}
b1 := p[1]
if b1 < accept.lo || accept.hi < b1 {
return RuneError, 1
}
if sz <= 2 { / <= instead of == to help the compiler eliminate some bounds checks
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 := int(x & 7)
accept := acceptRanges[x>>4]
if n < sz {
return RuneError, 1
}
s1 := s[1]
if s1 < accept.lo || accept.hi < s1 {
return RuneError, 1
}
if sz <= 2 { / <= instead of == to help the compiler eliminate some bounds checks
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.
/ If the rune is out of range, it writes the encoding of RuneError.
/ 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
}
}
/ AppendRune appends the UTF-8 encoding of r to the end of p and
/ returns the extended buffer. If the rune is out of range,
/ it appends the encoding of RuneError.
func AppendRune(p []byte, r rune) []byte {
/ This function is inlineable for fast handling of ASCII.
if uint32(r) <= rune1Max {
return append(p, byte(r))
}
return appendRuneNonASCII(p, r)
}
func appendRuneNonASCII(p []byte, r rune) []byte {
/ Negative values are erroneous. Making it unsigned addresses the problem.
switch i := uint32(r); {
case i <= rune2Max:
return append(p, t2|byte(r>>6), tx|byte(r)&maskx)
case i > MaxRune, surrogateMin <= i && i <= surrogateMax:
r = RuneError
fallthrough
case i <= rune3Max:
return append(p, t3|byte(r>>12), tx|byte(r>>6)&maskx, tx|byte(r)&maskx)
default:
return append(p, t4|byte(r>>18), tx|byte(r>>12)&maskx, tx|byte(r>>6)&maskx, tx|byte(r)&maskx)
}
}
/ 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 {
/ This optimization avoids the need to recompute the capacity
/ when generating code for p[8:], bringing it to parity with
/ ValidString, which was 20% faster on long ASCII strings.
p = p[:len(p):len(p)]
/ Fast path. Check for and skip 8 bytes of ASCII characters per iteration.
for len(p) >= 8 {
/ Combining two 32 bit loads allows the same code to be used
/ for 32 and 64 bit platforms.
/ The compiler can generate a 32bit load for first32 and second32
/ on many platforms. See test/codegen/memcombine.go.
first32 := uint32(p[0]) | uint32(p[1])<<8 | uint32(p[2])<<16 | uint32(p[3])<<24
second32 := uint32(p[4]) | uint32(p[5])<<8 | uint32(p[6])<<16 | uint32(p[7])<<24
if (first32|second32)&0x80808080 != 0 {
/ Found a non ASCII byte (>= RuneSelf).
break
}
p = p[8:]
}
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 {
/ Fast path. Check for and skip 8 bytes of ASCII characters per iteration.
for len(s) >= 8 {
/ Combining two 32 bit loads allows the same code to be used
/ for 32 and 64 bit platforms.
/ The compiler can generate a 32bit load for first32 and second32
/ on many platforms. See test/codegen/memcombine.go.
first32 := uint32(s[0]) | uint32(s[1])<<8 | uint32(s[2])<<16 | uint32(s[3])<<24
second32 := uint32(s[4]) | uint32(s[5])<<8 | uint32(s[6])<<16 | uint32(s[7])<<24
if (first32|second32)&0x80808080 != 0 {
/ Found a non ASCII byte (>= RuneSelf).
break
}
s = s[8:]
}
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
}