new file mode 100644
--- /dev/null
+++ b/pytouhou/utils/lzss.py
@@ -0,0 +1,25 @@
+def decompress(bitstream, size, dictionary_size=0x2000,
+               offset_size=13, length_size=4, minimum_match_length=3):
+    out_data = []
+    dictionary = [0] * dictionary_size
+    dictionary_head = 1
+    while len(out_data) < size:
+        flag = bitstream.read_bit()
+        if flag:
+            # The `flag` bit is set, indicating the upcoming chunk of data is a literal
+            # Add it to the uncompressed file, and store it in the dictionary
+            byte = bitstream.read(8)
+            dictionary[dictionary_head] = byte
+            dictionary_head = (dictionary_head + 1) % dictionary_size
+            out_data.append(byte)
+        else:
+            # The `flag` bit is not set, the upcoming chunk is a (offset, length) tuple
+            offset = bitstream.read(offset_size)
+            length = bitstream.read(length_size) + minimum_match_length
+            if (offset, length) == (0, 0):
+                break
+            for i in range(offset, offset + length):
+                out_data.append(dictionary[i % dictionary_size])
+                dictionary[dictionary_head] = dictionary[i % dictionary_size]
+                dictionary_head = (dictionary_head + 1) % dictionary_size
+    return b''.join(chr(byte) for byte in out_data)