go-utf8/readrune.go

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2022-07-18 23:36:02 +00:00
package utf8
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import (
"io"
)
// ReadRune reads a single UTF-8 encoded Unicode character from an io.Reader,
// and returns the Unicode character (as a Go rune) and the number of bytes read.
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//
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// If reader is nil then ReaderRune will return an error that matches utf8.NilReaderComplainer.
//
// Example
//
// Here is an example usage of ReadRune:
//
// r, n, err := utf8.ReadRune(reader)
// if nil != err {
//
// switch err.(type) {
// case utf8.NilReaderComplainer:
// //@TODO
// case utf8.InvalidUTF8Complainer:
// //@TODO
// default:
// //TODO
// }
//
// }
//
// Number Of Bytes
//
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// Note that a single UTF-8 encoded Unicode character could be more than one byte.
//
// 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) {
if nil == reader {
return 0, 0, errNilReader
}
var count int
var b0 byte
{
var buffer [1]byte
var p []byte = buffer[:]
n, err := reader.Read(p)
count += n
if nil != err {
return 0, count, err
}
if 1 != n {
return 0, count, errInternalError
}
b0 = buffer[0]
}
if 127 >= b0 {
return rune(b0), count, nil
}
var more int
{
switch {
// 110x,xxxx 110x,xxxx
// 0b1100,0000 == (0b1110,0000 & b0)
case 0xC0 == (0xE0 & b0):
more = 2-1
// 1110,xxxx 1110,xxxx
// 0b1110,0000 == (0b1111,0000 & b0)
case 0xE0 == (0xF0 & b0):
more = 3-1
// 1111,0xxx 1111,0xxx
// 0b1111,0000 == (0b1111,1000 & b0)
case 0xF0 == (0xF8 & b0):
more = 4-1
// 1111,10xx 1111,10xx
// 0b1111,1000 == (0b1111,1100 & b0)
case 0xF8 == (0xFC & b0):
more = 5-1
// 1111,110x 1111,110x
// 0b1111,1100 == (0b1111,1110 & b0)
case 0xFC == (0xFE & b0):
more = 6-1
// 1111,1111 1111,1111
// 0b1111,1110 == (0b1111,1111 & b0)
case 0xFE == (0xFF & b0):
more = 7-1
default:
return 0, count, errInternalError
}
}
var bs [6]byte
{
p := bs[:more]
n, err := reader.Read(p)
count += n
if nil != err {
return 0, count, err
}
if more != n {
return 0, count, errInternalError
}
}
var r rune
{
var b byte
switch {
// 110x,xxxx 110x,xxxx
// 0b1100,0000 == (0b1110,0000 & b0)
case 0xC0 == (0xE0 & b0):
b = (0xE0^0xFF) & b0
// 1110,xxxx 1110,xxxx
// 0b1110,0000 == (0b1111,0000 & b0)
case 0xE0 == (0xF0 & b0):
b = (0xF0^0xFF) & b0
// 1111,0xxx 1111,0xxx
// 0b1111,0000 == (0b1111,1000 & b0)
case 0xF0 == (0xF8 & b0):
b = (0xF8^0xFF) & b0
// 1111,10xx 1111,10xx
// 0b1111,1000 == (0b1111,1100 & b0)
case 0xF8 == (0xFC & b0):
b = (0xFC^0xFF) & b0
// 1111,110x 1111,110x
// 0b1111,1100 == (0b1111,1110 & b0)
case 0xFC == (0xFE & b0):
b = (0xFE^0xFF) & b0
// 1111,1111 1111,1111
// 0b1111,1110 == (0b1111,1111 & b0)
case 0xFE == (0xFF & b0):
//b := (0xFF^0xFF) & b0
default:
return 0, count, errInternalError
}
r = rune(b)
r <<= 6
for i:=0; i<more; i++ {
bsi := bs[i]
// if 0b1000,0000 != (0b0b1100,0000 & bsi) {
if 0x80 != (0xC0 & bsi) {
return 0, count, errInvalidUTF8
}
// b := 0b0011,1111 & bsi
b := 0x3F & bsi
r2 := rune(b)
r |= r2
if i < (more-1) {
r <<= 6
}
}
}
return r, count, nil
}