163 lines
2.9 KiB
Go
163 lines
2.9 KiB
Go
package utf8s
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import (
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"io"
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)
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// ReadRune reads a single UTF-8 encoded Unicode character from an io.Reader,
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// and returns the Unicode character (as a Go rune) and the number of bytes read.
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//
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// Note that a single UTF-8 encoded Unicode character could be more than one byte.
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//
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// For example, the Unicode "≡" (IDENTICAL TO) character gets encoded using 3 bytes under UTF-8.
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func ReadRune(reader io.Reader) (rune, int, error) {
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if nil == reader {
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return 0, 0, errNilReader
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}
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var count int
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var b0 byte
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{
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var buffer [1]byte
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var p []byte = buffer[:]
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n, err := reader.Read(p)
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count += n
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if nil != err {
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return 0, count, err
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}
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if 1 != n {
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return 0, count, errInternalError
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}
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b0 = buffer[0]
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}
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if 127 >= b0 {
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return rune(b0), count, nil
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}
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var more int
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{
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switch {
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// 110x,xxxx 110x,xxxx
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// 0b1100,0000 == (0b1110,0000 & b0)
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case 0xC0 == (0xE0 & b0):
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more = 2-1
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// 1110,xxxx 1110,xxxx
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// 0b1110,0000 == (0b1111,0000 & b0)
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case 0xE0 == (0xF0 & b0):
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more = 3-1
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// 1111,0xxx 1111,0xxx
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// 0b1111,0000 == (0b1111,1000 & b0)
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case 0xF0 == (0xF8 & b0):
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more = 4-1
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// 1111,10xx 1111,10xx
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// 0b1111,1000 == (0b1111,1100 & b0)
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case 0xF8 == (0xFC & b0):
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more = 5-1
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// 1111,110x 1111,110x
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// 0b1111,1100 == (0b1111,1110 & b0)
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case 0xFC == (0xFE & b0):
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more = 6-1
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// 1111,1111 1111,1111
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// 0b1111,1110 == (0b1111,1111 & b0)
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case 0xFE == (0xFF & b0):
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more = 7-1
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default:
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return 0, count, errInternalError
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}
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}
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var bs [6]byte
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{
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p := bs[:more]
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n, err := reader.Read(p)
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count += n
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if nil != err {
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return 0, count, err
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}
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if more != n {
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return 0, count, errInternalError
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}
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}
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var r rune
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{
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var b byte
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switch {
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// 110x,xxxx 110x,xxxx
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// 0b1100,0000 == (0b1110,0000 & b0)
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case 0xC0 == (0xE0 & b0):
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b = (0xE0^0xFF) & b0
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// 1110,xxxx 1110,xxxx
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// 0b1110,0000 == (0b1111,0000 & b0)
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case 0xE0 == (0xF0 & b0):
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b = (0xF0^0xFF) & b0
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// 1111,0xxx 1111,0xxx
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// 0b1111,0000 == (0b1111,1000 & b0)
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case 0xF0 == (0xF8 & b0):
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b = (0xF8^0xFF) & b0
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// 1111,10xx 1111,10xx
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// 0b1111,1000 == (0b1111,1100 & b0)
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case 0xF8 == (0xFC & b0):
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b = (0xFC^0xFF) & b0
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// 1111,110x 1111,110x
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// 0b1111,1100 == (0b1111,1110 & b0)
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case 0xFC == (0xFE & b0):
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b = (0xFE^0xFF) & b0
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// 1111,1111 1111,1111
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// 0b1111,1110 == (0b1111,1111 & b0)
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case 0xFE == (0xFF & b0):
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//b := (0xFF^0xFF) & b0
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default:
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return 0, count, errInternalError
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}
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r = rune(b)
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r <<= 6
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for i:=0; i<more; i++ {
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bsi := bs[i]
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// if 0b1000,0000 != (0b0b1100,0000 & bsi) {
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if 0x80 != (0xC0 & bsi) {
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return 0, count, errInvalidUTF8
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}
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// b := 0b0011,1111 & bsi
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b := 0x3F & bsi
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r2 := rune(b)
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r |= r2
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if i < (more-1) {
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r <<= 6
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}
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}
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}
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return r, count, nil
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}
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