// 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.
// Functions and constants to support text encoded in UTF-8.
// This package calls a Unicode character a rune for brevity.
package utf8
import "unicode" // only needed for a couple of constants
// Numbers fundamental to the encoding.
const (
RuneError = unicode.ReplacementChar; // the "error" Rune or "replacement character".
RuneSelf = 0x80; // characters below Runeself are represented as themselves in a single byte.
UTFMax = 4; // maximum number of bytes of a UTF-8 encoded Unicode character.
)
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) {
n := len(p);
if n < 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 n < 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 n < 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 n < 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;
}
func decodeRuneInStringInternal(s string) (rune, size int, short bool) {
n := len(s);
if n < 1 {
return RuneError, 0, true
}
c0 := s[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 n < 2 {
return RuneError, 1, true
}
c1 := s[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 n < 3 {
return RuneError, 1, true
}
c2 := s[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 n < 4 {
return RuneError, 1, true
}
c3 := s[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;
}
// FullRune reports whether the bytes in p begin with a full UTF-8 encoding of a rune.
// An invalid encoding is considered a full Rune since it will convert as a width-1 error rune.
func FullRune(p []byte) bool {
_, _, short := decodeRuneInternal(p);
return !short;
}
// FullRuneInString is like FullRune but its input is a string.
func FullRuneInString(s string) bool {
_, _, short := decodeRuneInStringInternal(s);
return !short;
}
// DecodeRune unpacks the first UTF-8 encoding in p and returns the rune and its width in bytes.
func DecodeRune(p []byte) (rune, size int) {
rune, size, _ = decodeRuneInternal(p);
return;
}
// DecodeRuneInString is like DecodeRune but its input is a string.
func DecodeRuneInString(s string) (rune, size int) {
rune, size, _ = decodeRuneInStringInternal(s);
return;
}
// RuneLen returns the number of bytes required to encode the rune.
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;
}
// EncodeRune writes into p (which must be large enough) the UTF-8 encoding of the rune.
// It returns the number of bytes written.
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 > unicode.MaxRune {
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;
}
// RuneCount returns the number of runes in p. Erroneous and short
// encodings are treated as single runes of width 1 byte.
func RuneCount(p []byte) int {
i := 0;
var n int;
for n = 0; i < len(p); n++ {
if p[i] < RuneSelf {
i++
} else {
_, size := DecodeRune(p[i:]);
i += size;
}
}
return n;
}
// RuneCountInString is like RuneCount but its input is a string.
func RuneCountInString(s string) (n int) {
for _ = range s {
n++
}
return;
}
// RuneStart reports whether the byte could be the first byte of
// an encoded rune. Second and subsequent bytes always have the top
// two bits set to 10.
func RuneStart(b byte) bool { return b&0xC0 != 0x80 }
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