1 files changed, 88 insertions, 0 deletions
diff --git a/modules/mahonia/kuten.go b/modules/mahonia/kuten.go
new file mode 100644
index 00000000..24929666
--- /dev/null
+++ b/modules/mahonia/kuten.go
@@ -0,0 +1,88 @@
+package mahonia
+
+import (
+	"sync"
+	"unicode/utf8"
+)
+
+// A kutenTable holds the data for a double-byte character set, arranged by ku
+// (区, zone) and ten (点, position). These can be converted to various actual
+// encoding schemes.
+type kutenTable struct {
+	// Data[ku][ten] is the unicode value for the character at that zone and
+	// position.
+	Data [94][94]uint16
+
+	// FromUnicode holds the ku and ten for each Unicode code point.
+	// It is not available until Reverse() has been called.
+	FromUnicode [][2]byte
+
+	// once is used to synchronize the generation of FromUnicode.
+	once sync.Once
+}
+
+// Reverse generates FromUnicode.
+func (t *kutenTable) Reverse() {
+	t.once.Do(func() {
+		t.FromUnicode = make([][2]byte, 65536)
+		for ku := range t.Data {
+			for ten, unicode := range t.Data[ku] {
+				t.FromUnicode[unicode] = [2]byte{byte(ku), byte(ten)}
+			}
+		}
+	})
+}
+
+// DecodeLow decodes a character from an encoding that does not have the high
+// bit set.
+func (t *kutenTable) DecodeLow(p []byte) (c rune, size int, status Status) {
+	if len(p) < 2 {
+		return 0, 0, NO_ROOM
+	}
+	ku := p[0] - 0x21
+	ten := p[1] - 0x21
+	if ku > 93 || ten > 93 {
+		return utf8.RuneError, 1, INVALID_CHAR
+	}
+	u := t.Data[ku][ten]
+	if u == 0 {
+		return utf8.RuneError, 1, INVALID_CHAR
+	}
+	return rune(u), 2, SUCCESS
+}
+
+// DecodeHigh decodes a character from an encoding that has the high bit set.
+func (t *kutenTable) DecodeHigh(p []byte) (c rune, size int, status Status) {
+	if len(p) < 2 {
+		return 0, 0, NO_ROOM
+	}
+	ku := p[0] - 0xa1
+	ten := p[1] - 0xa1
+	if ku > 93 || ten > 93 {
+		return utf8.RuneError, 1, INVALID_CHAR
+	}
+	u := t.Data[ku][ten]
+	if u == 0 {
+		return utf8.RuneError, 1, INVALID_CHAR
+	}
+	return rune(u), 2, SUCCESS
+}
+
+// EncodeHigh encodes a character in an encoding that has the high bit set.
+func (t *kutenTable) EncodeHigh(p []byte, c rune) (size int, status Status) {
+	if len(p) < 2 {
+		return 0, NO_ROOM
+	}
+	if c > 0xffff {
+		p[0] = '?'
+		return 1, INVALID_CHAR
+	}
+	kuten := t.FromUnicode[c]
+	if kuten == [2]byte{0, 0} && c != rune(t.Data[0][0]) {
+		p[0] = '?'
+		return 1, INVALID_CHAR
+	}
+	p[0] = kuten[0] + 0xa1
+	p[1] = kuten[1] + 0xa1
+	return 2, SUCCESS
+}