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package encoder
import "unicode/utf8"
const (
// The default lowest and highest continuation byte.
locb = 128 //0b10000000
hicb = 191 //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
}
const (
lineSep = byte(168) //'\u2028'
paragraphSep = byte(169) //'\u2029'
)
type decodeRuneState int
const (
validUTF8State decodeRuneState = iota
runeErrorState
lineSepState
paragraphSepState
)
func decodeRuneInString(s string) (decodeRuneState, int) {
n := len(s)
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.
if rune(s[0])&^mask|utf8.RuneError&mask == utf8.RuneError {
return runeErrorState, 1
}
return validUTF8State, 1
}
sz := int(x & 7)
if n < sz {
return runeErrorState, 1
}
s1 := s[1]
switch x >> 4 {
case 0:
if s1 < locb || hicb < s1 {
return runeErrorState, 1
}
case 1:
if s1 < 0xA0 || hicb < s1 {
return runeErrorState, 1
}
case 2:
if s1 < locb || 0x9F < s1 {
return runeErrorState, 1
}
case 3:
if s1 < 0x90 || hicb < s1 {
return runeErrorState, 1
}
case 4:
if s1 < locb || 0x8F < s1 {
return runeErrorState, 1
}
}
if sz <= 2 {
return validUTF8State, 2
}
s2 := s[2]
if s2 < locb || hicb < s2 {
return runeErrorState, 1
}
if sz <= 3 {
// separator character prefixes: [2]byte{226, 128}
if s0 == 226 && s1 == 128 {
switch s2 {
case lineSep:
return lineSepState, 3
case paragraphSep:
return paragraphSepState, 3
}
}
return validUTF8State, 3
}
s3 := s[3]
if s3 < locb || hicb < s3 {
return runeErrorState, 1
}
return validUTF8State, 4
}
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