Refactor repository layout and convert build system to Mage.

This commit implements a massive refactor of the repository, and
moves the build system over to use Mage (magefile.org) which should
allow seamless building across multiple platforms.

vendor/github.com/nwaples/rardecode/decode29_ppm.go

@@ -0,0 +1,132 @@
+package rardecode
+
+import "io"
+
+type ppm29Decoder struct {
+	m   model // ppm model
+	esc byte  // escape character
+	br  io.ByteReader
+}
+
+func (d *ppm29Decoder) init(br *rarBitReader) error {
+	maxOrder, err := br.readBits(7)
+	if err != nil {
+		return err
+	}
+	reset := maxOrder&0x20 > 0
+
+	// Should have flushed all unread bits from bitReader by now,
+	// use underlying ByteReader
+	d.br = br.r
+
+	var maxMB int
+	if reset {
+		c, err := d.br.ReadByte()
+		if err != nil {
+			return err
+		}
+		maxMB = int(c) + 1
+	}
+
+	if maxOrder&0x40 > 0 {
+		d.esc, err = d.br.ReadByte()
+		if err != nil {
+			return err
+		}
+	}
+
+	maxOrder = (maxOrder & 0x1f) + 1
+	if maxOrder > 16 {
+		maxOrder = 16 + (maxOrder-16)*3
+	}
+
+	return d.m.init(d.br, reset, maxOrder, maxMB)
+}
+
+func (d *ppm29Decoder) reset() {
+	d.esc = 2
+}
+
+func (d *ppm29Decoder) readFilterData() ([]byte, error) {
+	c, err := d.m.ReadByte()
+	if err != nil {
+		return nil, err
+	}
+	n := int(c&7) + 1
+	if n == 7 {
+		b, err := d.m.ReadByte()
+		if err != nil {
+			return nil, err
+		}
+		n += int(b)
+	} else if n == 8 {
+		b, err := d.m.ReadByte()
+		if err != nil {
+			return nil, err
+		}
+		n = int(b) << 8
+		b, err = d.m.ReadByte()
+		if err != nil {
+			return nil, err
+		}
+		n |= int(b)
+	}
+
+	n++
+	buf := make([]byte, n)
+	buf[0] = byte(c)
+	for i := 1; i < n; i++ {
+		buf[i], err = d.m.ReadByte()
+		if err != nil {
+			return nil, err
+		}
+	}
+	return buf, nil
+}
+
+func (d *ppm29Decoder) decode(w *window) ([]byte, error) {
+	c, err := d.m.ReadByte()
+	if err != nil {
+		return nil, err
+	}
+	if c != d.esc {
+		w.writeByte(c)
+		return nil, nil
+	}
+	c, err = d.m.ReadByte()
+	if err != nil {
+		return nil, err
+	}
+
+	switch c {
+	case 0:
+		return nil, endOfBlock
+	case 2:
+		return nil, endOfBlockAndFile
+	case 3:
+		return d.readFilterData()
+	case 4:
+		offset := 0
+		for i := 0; i < 3; i++ {
+			c, err = d.m.ReadByte()
+			if err != nil {
+				return nil, err
+			}
+			offset = offset<<8 | int(c)
+		}
+		len, err := d.m.ReadByte()
+		if err != nil {
+			return nil, err
+		}
+		w.copyBytes(int(len)+32, offset+2)
+	case 5:
+		len, err := d.m.ReadByte()
+		if err != nil {
+			return nil, err
+		}
+		w.copyBytes(int(len)+4, 1)
+	default:
+		w.writeByte(d.esc)
+	}
+	return nil, nil
+}