Add files

src/tools/pb16.py

@@ -0,0 +1,76 @@
+#!/usr/bin/env python
+"""
+PB16 encoder
+Copyright 2018 Damian Yerrick
+[License: zlib]
+
+PB16 can be thought of as either of two things:
+
+- Run-length encoding (RLE) of two interleaved streams, with
+  unary-coded run lengths
+- LZSS with a fixed distance of 2 and a fixed copy length of 1
+
+Each packet represents 8 bytes of uncompressed data.  The bits
+of the first byte in a packet, ordered from MSB to LSB, encode
+which of the following eight bytes repeat the byte 2 bytes back.
+A 0 means a literal byte follows; a 1 means a repeat.
+
+It's similar to the PB8 codec that I've used for NES CHR data,
+adapted to the interleaving of Game Boy and Super NES CHR data.
+"""
+import itertools
+import sys
+import argparse
+
+def ichunk(data, count):
+    """Turn an iterable into lists of a fixed length."""
+    data = iter(data)
+    while True:
+        b = list(itertools.islice(data, count))
+        if len(b) == 0: break
+        yield b
+
+def pb16(data):
+    """Compress an iterable of bytes into a generator of PB16 packets."""
+    prev = [0, 0]
+    for unco in ichunk(data, 8):
+        # Pad the chunk to a multiple of 2 then to 8 bytes
+        if len(unco) < 8:
+            if len(unco) == 1:
+                unco.append(prev[1])
+            elif len(unco) % 2:
+                unco.append(unco[-2])
+            unco.extend(unco[-2:]*(8 - len(unco)))
+
+        packet = bytearray(1)
+        for i, value in enumerate(unco):
+            if value == prev[i % 2]:
+                packet[0] |= 0x80 >> i
+            else:
+                packet.append(value)
+                prev[i % 2] = value
+        yield packet
+
+def parse_argv(argv):
+    p = argparse.ArgumentParser()
+    p.add_argument("infile")
+    p.add_argument("outfile")
+    return p.parse_args(argv[1:])
+
+def main(argv=None):
+    args = parse_argv(argv or sys.argv)
+    with open(args.infile, "rb") as infp:
+        data = infp.read()
+    with open(args.outfile, "wb") as outfp:
+        outfp.writelines(pb16(data))
+
+def test():
+    tests = [
+        ()
+    ]
+    s = b"ABAHBHCHCECEFEFE"
+    print(b''.join(pb16(s)).hex())
+
+if __name__=='__main__':
+    main()
+##    test()