new file mode 100644
--- /dev/null
+++ b/pytouhou/utils/bitstream.py
@@ -0,0 +1,57 @@
+class BitStream(object):
+    def __init__(self, io):
+        self.io = io
+        self.bits = 0
+        self.byte = 0
+
+
+    def seek(self, offset, whence=0):
+        self.io.seek(offset, whence)
+        self.byte = 0
+        self.bits = 0
+
+
+    def tell(self):
+        return self.io.tell()
+
+
+    def tell2(self):
+        return self.io.tell(), self.bits
+
+
+    def read_bit(self):
+        if not self.bits:
+            self.byte = ord(self.io.read(1))
+            self.bits = 8
+        self.bits -= 1
+        return (self.byte >> self.bits) & 0x01
+
+
+    def read(self, nb_bits):
+        value = 0
+        for i in range(nb_bits - 1, -1, -1):
+            value |= self.read_bit() << i
+        return value
+
+
+    def write_bit(self, bit):
+        if self.bits == 8:
+            self.io.write(chr(self.byte))
+            self.bits = 0
+            self.byte = 0
+        self.byte &= ~(1 << (7 - self.bits))
+        self.byte |= bit << (7 - self.bits)
+        self.bits += 1
+
+
+    def write(self, bits, nb_bits):
+        for i in range(nb_bits):
+            self.write_bit(bits >> (nb_bits - 1 - i) & 0x01)
+
+
+    def flush(self):
+        self.io.write(chr(self.byte))
+        self.bits = 0
+        self.byte = 0
+        self.io.flush()
+