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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// UTF-8 support.
package utf8
export const (
UTFMax = 4;
RuneError = 0xFFFD;
RuneSelf = 0x80;
RuneMax = 1<<21 - 1;
)
const (
T1 = 0x00; // 0000 0000
Tx = 0x80; // 1000 0000
T2 = 0xC0; // 1100 0000
T3 = 0xE0; // 1110 0000
T4 = 0xF0; // 1111 0000
T5 = 0xF8; // 1111 1000
Maskx = 0x3F; // 0011 1111
Mask2 = 0x1F; // 0001 1111
Mask3 = 0x0F; // 0000 1111
Mask4 = 0x07; // 0000 0111
Rune1Max = 1<<7 - 1;
Rune2Max = 1<<11 - 1;
Rune3Max = 1<<16 - 1;
Rune4Max = 1<<21 - 1;
)
func DecodeRuneInternal(p *[]byte) (rune, size int, short bool) {
if len(p) < 1 {
return RuneError, 0, true;
}
c0 := p[0];
// 1-byte, 7-bit sequence?
if c0 < Tx {
return int(c0), 1, false
}
// unexpected continuation byte?
if c0 < T2 {
return RuneError, 1, false
}
// need first continuation byte
if len(p) < 2 {
return RuneError, 1, true
}
c1 := p[1];
if c1 < Tx || T2 <= c1 {
return RuneError, 1, false
}
// 2-byte, 11-bit sequence?
if c0 < T3 {
rune = int(c0&Mask2)<<6 | int(c1&Maskx);
if rune <= Rune1Max {
return RuneError, 1, false
}
return rune, 2, false
}
// need second continuation byte
if len(p) < 3 {
return RuneError, 1, true
}
c2 := p[2];
if c2 < Tx || T2 <= c2 {
return RuneError, 1, false
}
// 3-byte, 16-bit sequence?
if c0 < T4 {
rune = int(c0&Mask3)<<12 | int(c1&Maskx)<<6 | int(c2&Maskx);
if rune <= Rune2Max {
return RuneError, 1, false
}
return rune, 3, false
}
// need third continuation byte
if len(p) < 4 {
return RuneError, 1, true
}
c3 := p[3];
if c3 < Tx || T2 <= c3 {
return RuneError, 1, false
}
// 4-byte, 21-bit sequence?
if c0 < T5 {
rune = int(c0&Mask4)<<18 | int(c1&Maskx)<<12 | int(c2&Maskx)<<6 | int(c3&Maskx);
if rune <= Rune3Max {
return RuneError, 1, false
}
return rune, 4, false
}
// error
return RuneError, 1, false
}
export func FullRune(p *[]byte) bool {
rune, size, short := DecodeRuneInternal(p);
return !short
}
export func DecodeRune(p *[]byte) (rune, size int) {
var short bool;
rune, size, short = DecodeRuneInternal(p);
return;
}
export func RuneLen(rune int) int {
switch {
case rune <= Rune1Max:
return 1;
case rune <= Rune2Max:
return 2;
case rune <= Rune3Max:
return 3;
case rune <= Rune4Max:
return 4;
}
return -1;
}
export func EncodeRune(rune int, p *[]byte) int {
if rune <= Rune1Max {
p[0] = byte(rune);
return 1;
}
if rune <= Rune2Max {
p[0] = T2 | byte(rune>>6);
p[1] = Tx | byte(rune)&Maskx;
return 2;
}
if rune > RuneMax {
rune = RuneError
}
if rune <= Rune3Max {
p[0] = T3 | byte(rune>>12);
p[1] = Tx | byte(rune>>6)&Maskx;
p[2] = Tx | byte(rune)&Maskx;
return 3;
}
p[0] = T4 | byte(rune>>18);
p[1] = Tx | byte(rune>>12)&Maskx;
p[2] = Tx | byte(rune>>6)&Maskx;
p[3] = Tx | byte(rune)&Maskx;
return 4;
}
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