Move RLE decoding into a separate package

internal/data/rle/rle.go

@@ -0,0 +1,60 @@
+// Package rle implements the run-length encoding scheme discovered in Chaos
+// Gate .obj files. It may be used for other data too - to be determined.
+package rle
+
+import (
+	"bufio"
+	"io"
+	"io/ioutil"
+)
+
+// Expand converts the compressed input data into uncompressed output data. The
+// output buffer should be of at least the expected size. We will read until
+// io.EOF is encountered.
+func Expand(in io.Reader, out []byte) error {
+	buf := bufio.NewReader(in)
+	idx := 0
+
+	for {
+		b, err := buf.ReadByte()
+		if err != nil {
+			if err == io.EOF {
+				return nil
+			}
+
+			return err
+		}
+
+		if b == 0x00 { // NOP
+			continue
+		} else if b < 0x80 { // repeat the next byte this many times
+			repeat := b
+			value, err := buf.ReadByte()
+			if err != nil {
+				return err
+			}
+
+			for x := 0; x < int(repeat); x++ {
+				out[idx+x] = value
+			}
+			idx = idx + int(repeat)
+		} else if b == 0x80 { // skip forward in the output by the next byte's value
+			skip, err := buf.ReadByte()
+			if err != nil {
+				return err
+			}
+
+			idx = idx + int(skip)
+		} else { // Take the next b-0x80 bytes literally
+			lr := io.LimitReader(buf, int64(b-0x80))
+			literals, err := ioutil.ReadAll(lr)
+			if err != nil {
+				return err
+			}
+			copy(out[idx:], literals)
+			idx = idx + len(literals)
+		}
+	}
+
+	return nil
+}