1 files changed, 46 insertions, 0 deletions
diff --git a/tools/xor_compress.py b/tools/xor_compress.py
new file mode 100644
index 0000000..30418db
--- /dev/null
+++ b/tools/xor_compress.py
@@ -0,0 +1,46 @@
+#!/usr/bin/env python3
+
+# Usage: ./xor_compress.py [source.bin] [dest.bin.xor]
+
+import sys
+
+with (open(sys.argv[1], 'rb') if len(sys.argv) > 1 else sys.stdin) as f:
+    data = f.read()
+
+n = len(data) 
+output = []
+v = 0
+i = 0
+
+while i < n:
+    val = data[i]
+    i += 1
+
+    if data[i] == v: #>=0x80
+        # Alternating (>= 0x80)
+        # Run stops at 0x81 bytes or when the values stop alternating
+        size = 1
+        while i < n and size < 0x81 and data[i] == (v if size % 2 else val):
+            size += 1
+            i += 1
+        output.append(size + 0x7e)
+        output.append(v ^ val)
+        if size % 2:
+            v = val
+
+    else:
+        # Sequential (< 0x80)
+        # Run stops at 0x80 bytes or when the value two ahead is equal to v
+        buffer = [v ^ val]
+        while i < n:
+            v = val
+            if len(buffer) > 0x7f or (i + 1 < n and data[i + 1] == v):
+                break
+            val = data[i]
+            buffer.append(v ^ val)
+            i += 1
+        output.append(len(buffer) - 1)
+        output.extend(buffer)
+
+with (open(sys.argv[2], 'wb') if len(sys.argv) > 2 else sys.stdout) as f:
+    f.write(bytes(output))