# HG changeset patch
# User Thibaut Girka <thib@sitedethib.com>
# Date 1312532354 -7200
# Node ID 776453783743bb3919ce566256a09cf8b7ebd217
# Parent  548662d708603f9331cd43349ad8793e929dfc5a
Add PRNG reverse-engineered from EoSD's 102h.exe.

diff --git a/pytouhou/utils/random.py b/pytouhou/utils/random.py
new file mode 100644
--- /dev/null
+++ b/pytouhou/utils/random.py
@@ -0,0 +1,36 @@
+"""
+This file provides a pseudo-random number generator identical to the one used in
+Touhou 6: The Embodiment of Scarlet Devil.
+It is the only truly reverse-engineered piece of code of this project,
+as it is needed in order to retain compatibility with replay files produced by
+the offical game code.
+
+It has been reverse engineered from 102h.exe@0x41e780."""
+
+
+#TODO: maybe some post-processing is missing
+
+
+from time import time
+
+class Random(object):
+    def __init__(self, seed=None):
+        if seed is None:
+            seed = int(time.time() % 65536)
+        self.counter = 0
+
+
+    def set_seed(self, seed):
+        self.seed = seed
+        self.counter = 0
+
+
+    def cycle(self):
+        # Named this way because the actual return value may be different.
+        # Further reverse engineering might be needed.
+        x = ((seed ^ 0x9630) - 0x6553) & 0xffff
+        self.seed = (((x & 0x0c000) >> 0xe) + x*4) & 0xffff
+        self.counter += 1
+        self.counter &= 0xffff
+        return self.seed
+