1 files changed, 291 insertions, 0 deletions
diff --git a/src/pkg/utf8/utf8.go b/src/pkg/utf8/utf8.go
new file mode 100644
index 000000000..9c2ac790d
--- /dev/null
+++ b/src/pkg/utf8/utf8.go
@@ -0,0 +1,291 @@
+// 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
+
+// Numbers fundamental to the encoding.
+const (
+	RuneError = 0xFFFD;	// the "error" Rune or "replacement character".
+	RuneSelf = 0x80;	// characters below Runeself are represented as themselves in a single byte.
+	RuneMax = 0x10FFFF;	// maximum Unicode code point.
+	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 {
+	rune, size, short := decodeRuneInternal(p);
+	return !short
+}
+
+// FullRuneInString is like FullRune but its input is a string.
+func FullRuneInString(s string) bool {
+	rune, size, 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) {
+	var short bool;
+	rune, size, short = decodeRuneInternal(p);
+	return;
+}
+
+// DecodeRuneInString is like DecodeRune but its input is a string.
+func DecodeRuneInString(s string) (rune, size int) {
+	var short bool;
+	rune, size, short = 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 > 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;
+}
+
+// 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 {
+			rune, size := DecodeRune(p[i:len(p)]);
+			i += size;
+		}
+	}
+	return n;
+}
+
+// RuneCountInString is like RuneCount but its input is a string.
+func RuneCountInString(s string) int {
+	ei := len(s);
+	i := 0;
+	n := 0;
+	for n = 0; i < ei; n++ {
+		if s[i] < RuneSelf {
+			i++;
+		} else {
+			rune, size, short := decodeRuneInStringInternal(s[i:ei]);
+			i += size;
+		}
+	}
+	return n;
+}
+