From e556a9624c67733c32329a095f6f508ea7b42a15 Mon Sep 17 00:00:00 2001
From: Emery Hemingway <emery@vfemail.net>
Date: Tue, 24 Jun 2014 20:11:46 -0400
Subject: [PATCH] yijing: initial commit, encoding only

---
 yijing/README.md      |   7 +++
 yijing/yijing.go      | 110 ++++++++++++++++++++++++++++++++++++++++++
 yijing/yijing_test.go |  54 +++++++++++++++++++++
 3 files changed, 171 insertions(+)
 create mode 100644 yijing/README.md
 create mode 100644 yijing/yijing.go
 create mode 100644 yijing/yijing_test.go

diff --git a/yijing/README.md b/yijing/README.md
new file mode 100644
index 0000000..d396001
--- /dev/null
+++ b/yijing/README.md
@@ -0,0 +1,7 @@
+A sha256 digest in hex
+
+  e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852
+
+A sha256 digest in git status in Yi Jing
+
+  ䷸䷻䷌䷄䷐䷩䷯䷼䷇䷁䷙䷚䷾䷿䷜䷈䷦䷖䷿䷹䷉䷂䷞䷮䷐䷞䷖䷤䷦䷹䷌䷌䷩䷉䷝䷙䷆䷷䷥䷒䷮䷅☲¦
diff --git a/yijing/yijing.go b/yijing/yijing.go
new file mode 100644
index 0000000..3914779
--- /dev/null
+++ b/yijing/yijing.go
@@ -0,0 +1,110 @@
+// Copyright 2014 Emery Hemingway. All rights reserved.
+// Use of this source code is governed by the GPLv3+.
+
+// Package yijing64 implements radix 64 Yijing encoding and decoding.
+package yijing
+
+// ䷀ 0xE4 0xB7 0x80
+// ䷿ 0xE4 0xB7 0xBF
+
+// ☰ 0xE2 0x98 0xb0
+// ☷ 0xE2 0x98 0xb8
+
+// ǀ 0xC7 0x80
+// ¦ 0xC2 0xa6
+
+// full block is 0xE2, 0x96, 0x88
+
+// EncodedLen returns the length of an encoding of n source bytes.
+func EncodedLen(n int) (l int) {
+	if n == 0 {
+		return 0
+	}
+
+	l = ((n * 4) / 3) * 3
+
+	switch n % 3 {
+	case 0:
+	case 1:
+		l += 4
+	case 2:
+		l += 5
+	}
+	return l
+}
+
+// Encode encodes src into EncodedLen(len(src))
+// bytes of dst.  As a convenience, it returns the number
+// of bytes written to dst, but this value is always EncodedLen(len(src)).
+// Encode implements Yi Jing encoding.
+func Encode(dst, src []byte) (n int) {
+	for len(src) > 0 {
+		dst[0] = 0xE4
+		dst[1] = 0xB7
+		dst[2] = 0x80 | (src[0] >> 2)
+
+		switch len(src) {
+
+		case 2:
+			dst[3] = 0xE4
+			dst[4] = 0xB7
+			dst[5] = 0x80 | ((src[0] & 0x03) << 4) | (src[1] >> 4)
+
+			dst[6] = 0xE2
+			dst[7] = 0x98
+			dst[8] = 0xB0 | ((src[1] & 0x0F) >> 1)
+
+			if (src[1] & 0xFE) == 0 {
+				dst[9] = 0xC7
+				dst[10] = 0x80
+			} else {
+				dst[9] = 0xC2
+				dst[10] = 0xA6
+			}
+			return n + 11
+
+		case 1:
+			if (src[0] & 0x02) == 0 {
+				dst[3] = 0xC7
+				dst[4] = 0x80
+			} else {
+				dst[3] = 0xC2
+				dst[4] = 0xA6
+			}
+
+			if (src[0] & 0x01) == 0 {
+				dst[5] = 0xC7
+				dst[6] = 0x80
+			} else {
+				dst[5] = 0xC2
+				dst[6] = 0xA6
+			}
+			return n + 7
+		}
+
+		dst[3] = 0xE4
+		dst[4] = 0xB7
+		dst[5] = 0x80 | ((src[0] & 0x03) << 4) | (src[1] >> 4)
+
+		dst[6] = 0xE4
+		dst[7] = 0xB7
+		dst[8] = 0x80 | ((src[1] & 0x0F) << 2) | (src[2] >> 4)
+
+		dst[9] = 0xE4
+		dst[10] = 0xB7
+		dst[11] = 0x80 | (src[2] & 0x3F)
+
+		n += 12
+
+		src = src[3:]
+		dst = dst[12:]
+	}
+	return n
+}
+
+// EncodeToString returns the Yi Jing encoding of src.
+func EncodeToString(src []byte) string {
+	dst := make([]byte, EncodedLen(len(src)))
+	Encode(dst, src)
+	return string(dst)
+}
diff --git a/yijing/yijing_test.go b/yijing/yijing_test.go
new file mode 100644
index 0000000..590f683
--- /dev/null
+++ b/yijing/yijing_test.go
@@ -0,0 +1,54 @@
+package yijing
+
+import (
+	"testing"
+)
+
+type encDecTest struct {
+	enc string
+	dec []byte
+}
+
+var encDecTests = []encDecTest{
+	{"", []byte{}},
+	{"䷀ǀǀ", []byte{0x00}},
+	{"䷿¦¦", []byte{0xFF}},
+	{"䷀䷀☰ǀ", []byte{0x00, 0x00}},
+	{"䷿䷿☷¦", []byte{0xFF, 0xFF}},
+	{"䷀䷀䷀䷀", []byte{0x00, 0x00, 0x00}},
+	{"䷕䷕䷕䷕", []byte{0x55, 0x55, 0x55}},
+	{"䷪䷪䷪䷪", []byte{0xAA, 0xAA, 0xAA}},
+	{"䷿䷿䷿䷿", []byte{0xFF, 0xFF, 0xFF}},
+	{"䷀䷀䷀䷀䷀䷀䷀䷀", []byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x00}},
+	{"䷿䷿䷿䷿䷿䷿䷿䷿", []byte{0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF}},
+}
+
+func TestEncode(t *testing.T) {
+	for i, test := range encDecTests {
+		dst := make([]byte, EncodedLen(len(test.dec)))
+		n := Encode(dst, test.dec)
+		if n != len(dst) {
+			t.Errorf("#%d: bad return value: got: %d want: %d", i, n, len(dst))
+		}
+		if string(dst) != test.enc {
+			t.Errorf("#%d: got: %q want: %q", i, dst, test.enc)
+		}
+	}
+}
+
+func BenchmarkEncode(b *testing.B) {
+	var c byte
+	for i := 0; i < b.N; i++ {
+		srcBuf := make([]byte, 27)
+		dstBuf := make([]byte, EncodedLen(27))
+		for l := 0; l < 28; l++ {
+			src := srcBuf[:l]
+			for ; c < 255; c++ {
+				for j := 0; j < l; j++ {
+					src[j] = c
+					Encode(dstBuf, src)
+				}
+			}
+		}
+	}
+}