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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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