From 5d91b2b59f63a9b3cb739943f2fadf03fef0d33f Mon Sep 17 00:00:00 2001
From: derrod <xlnedder@gmail.com>
Date: Wed, 6 May 2020 19:49:45 +0200
Subject: [PATCH] [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 | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)
 create mode 100644 legendary/utils/rolling_hash.py

diff --git a/legendary/utils/rolling_hash.py b/legendary/utils/rolling_hash.py
new file mode 100644
index 0000000..eb89034
--- /dev/null
+++ b/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