[utils] Add FRollingHash implementation

Seems to be a variation on CRC-64-ECMA.
This python version is of course very slow.
That should not be a big issue however, since
it is only required for serialising rather
small save game data.

legendary/utils/rolling_hash.py

@@ -0,0 +1,25 @@
+# this is the rolling hash Epic uses, it appears to be a variation on CRC-64-ECMA
+
+hash_poly = 0xC96C5795D7870F42
+hash_table = []
+
+
+def _init():
+    for i in range(256):
+        for _ in range(8):
+            if i & 1:
+                i >>= 1
+                i ^= hash_poly
+            else:
+                i >>= 1
+        hash_table.append(i)
+
+
+def get_hash(data):
+    if not hash_table:
+        _init()
+
+    h = 0
+    for i in range(len(data)):
+        h = ((h << 1 | h >> 63) ^ hash_table[c.data[i]]) & 0xffffffffffffffff
+    return h