add endfield support

vfs.py

@@ -0,0 +1,53 @@
+# decrypt and parse endfield's .chk files for audio
+
+def decrypt(data, offset, count, seed, fileOffset):
+	keySeed = seed + (fileOffset >> 2)
+
+	dataIndex = offset
+	remaining = count
+	alignement = fileOffset & 3
+
+	# head
+	if alignement != 0:
+		keyValue = key(keySeed)
+		toAlign = min(4 - alignement, remaining)
+
+		for i in range(toAlign):
+			if dataIndex >= offset + count:
+				break
+			bytePos = alignement + i
+			data[dataIndex] ^= (keyValue >> (bytePos * 8)) & 0xFF
+			dataIndex += 1
+
+		remaining -= toAlign
+		keySeed += 1
+
+	# body
+	nBlocks = remaining // 4
+
+	for i in range(nBlocks):
+		keyValue = key(keySeed)
+		dataValue = int.from_bytes(data[dataIndex:dataIndex+4], "little") ^ keyValue
+
+		data[dataIndex] = dataValue & 0xFF
+		data[dataIndex+1] = (dataValue >> 8) & 0xFF
+		data[dataIndex+2] = (dataValue >> 16) & 0xFF
+		data[dataIndex+3] = (dataValue >> 24) & 0xFF
+		
+		dataIndex += 4
+		keySeed += 1
+
+	# tail
+	trailing = remaining & 3
+	if trailing > 0:
+		keyValue = key(keySeed)
+		for i in range(trailing):
+			data[dataIndex] ^= (keyValue >> (i * 8)) & 0xFF
+			dataIndex += 1
+
+def key(seed):
+	k = ((((seed & 0xFF) ^ 0x9C5A0B29) & 0xFFFFFFFF) * 81861667) & 0xFFFFFFFF
+	k = ((k ^ ((seed >> 8) & 0xFF)) * 81861667) & 0xFFFFFFFF
+	k = ((k ^ ((seed >> 16) & 0xFF)) * 81861667) & 0xFFFFFFFF
+	k = ((k ^ (seed >> 24) & 0xFF) * 81861667) & 0xFFFFFFFF
+	return k