forked from mirror/go-json
128 lines
3.8 KiB
Go
128 lines
3.8 KiB
Go
package encoder
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import "unicode/utf8"
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const (
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// The default lowest and highest continuation byte.
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locb = 128 //0b10000000
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hicb = 191 //0b10111111
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// These names of these constants are chosen to give nice alignment in the
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// table below. The first nibble is an index into acceptRanges or F for
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// special one-byte cases. The second nibble is the Rune length or the
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// Status for the special one-byte case.
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xx = 0xF1 // invalid: size 1
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as = 0xF0 // ASCII: size 1
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s1 = 0x02 // accept 0, size 2
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s2 = 0x13 // accept 1, size 3
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s3 = 0x03 // accept 0, size 3
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s4 = 0x23 // accept 2, size 3
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s5 = 0x34 // accept 3, size 4
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s6 = 0x04 // accept 0, size 4
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s7 = 0x44 // accept 4, size 4
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)
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// first is information about the first byte in a UTF-8 sequence.
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var first = [256]uint8{
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// 1 2 3 4 5 6 7 8 9 A B C D E F
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as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x00-0x0F
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as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x10-0x1F
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as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x20-0x2F
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as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x30-0x3F
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as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x40-0x4F
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as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x50-0x5F
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as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x60-0x6F
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as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x70-0x7F
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// 1 2 3 4 5 6 7 8 9 A B C D E F
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xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0x80-0x8F
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xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0x90-0x9F
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xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xA0-0xAF
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xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xB0-0xBF
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xx, xx, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, // 0xC0-0xCF
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s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, // 0xD0-0xDF
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s2, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s4, s3, s3, // 0xE0-0xEF
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s5, s6, s6, s6, s7, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xF0-0xFF
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}
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// acceptRange gives the range of valid values for the second byte in a UTF-8
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// sequence.
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type acceptRange struct {
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lo uint8 // lowest value for second byte.
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hi uint8 // highest value for second byte.
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}
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var (
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sep = [2]byte{226, 128}
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lineSep = byte(168) //'\u2028'
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paragraphSep = byte(169) //'\u2029'
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)
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type decodeRuneState int
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const (
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validUTF8State decodeRuneState = iota
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runeErrorState
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lineSepState
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paragraphSepState
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)
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func decodeRuneInString(s string) (decodeRuneState, int) {
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n := len(s)
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s0 := s[0]
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x := first[s0]
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if x >= as {
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// The following code simulates an additional check for x == xx and
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// handling the ASCII and invalid cases accordingly. This mask-and-or
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// approach prevents an additional branch.
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mask := rune(x) << 31 >> 31 // Create 0x0000 or 0xFFFF.
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if rune(s[0])&^mask|utf8.RuneError&mask == utf8.RuneError {
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return runeErrorState, 1
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}
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return validUTF8State, 1
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}
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sz := int(x & 7)
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var accept acceptRange
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switch x >> 4 {
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case 0:
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accept = acceptRange{locb, hicb}
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case 1:
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accept = acceptRange{0xA0, hicb}
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case 2:
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accept = acceptRange{locb, 0x9F}
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case 3:
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accept = acceptRange{0x90, hicb}
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case 4:
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accept = acceptRange{locb, 0x8F}
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}
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if n < sz {
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return runeErrorState, 1
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}
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s1 := s[1]
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if s1 < accept.lo || accept.hi < s1 {
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return runeErrorState, 1
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}
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if sz <= 2 {
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return validUTF8State, 2
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}
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s2 := s[2]
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if s2 < locb || hicb < s2 {
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return runeErrorState, 1
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}
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if sz <= 3 {
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if s[0] == sep[0] && s[1] == sep[1] {
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switch s[2] {
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case lineSep:
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return lineSepState, 3
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case paragraphSep:
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return paragraphSepState, 3
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}
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}
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return validUTF8State, 3
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}
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s3 := s[3]
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if s3 < locb || hicb < s3 {
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return runeErrorState, 1
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}
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return validUTF8State, 4
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}
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