1 files changed, 162 insertions, 0 deletions
diff --git a/src/lib/utf8.go b/src/lib/utf8.go
new file mode 100644
index 000000000..7b0f15d8f
--- /dev/null
+++ b/src/lib/utf8.go
@@ -0,0 +1,162 @@
+// 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 (
+	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;
+}
+