Réécriture de M_R en Python

1 files changed, 26 insertions, 15 deletions

diff --git a/src/add_python/lilliput/multiplications.py b/src/add_python/lilliput/multiplications.py
index c5abdfc..8ca8c7f 100644
--- a/src/add_python/lilliput/multiplications.py
+++ b/src/add_python/lilliput/multiplications.py
@@ -76,24 +76,35 @@ M3 = (
 )
 
 
-def _multiplication(m):
-    def _multiply(x):
-        return list(reversed([
-            reduce(xor, (mj[i](xi) for i, xi in enumerate(reversed(x))))
-            for mj in m
-        ]))
-
-    return _multiply
+# NB: shift directions are reversed with respect to the specification
+# for powers of M_R, since the specification reverses the byte order
+# for those matrices.
+
+MR = (
+    ( _0, _Id,  _0,     _0,     _0,  _0,     _0,  _0),
+    ( _0,  _0, _Id,     _0,     _0,  _0,     _0,  _0),
+    ( _0,  _0,  _0,    _Id, _Sr(3),  _0,     _0,  _0),
+    ( _0,  _0,  _0,     _0,    _Id,  _0,     _0,  _0),
+    ( _0,  _0,  _0,     _0,     _0, _Id, _Sl(3),  _0),
+    ( _0,  _0,  _0, _Sl(2),     _0,  _0,    _Id,  _0),
+    ( _0,  _0,  _0,     _0,     _0,  _0,     _0, _Id),
+    (_Id,  _0,  _0,     _0,     _0,  _0,     _0,  _0),
+)
 
 
-def _multiply_MR(lane):
-    multiplied_lane = [lane[(byte+1) % 8] for byte in range(0, 8)]
+def _multiplication(m, reverse=True):
+    def ordered(l):
+        if reverse:
+            return list(reversed(list(l)))
+        return l
 
-    multiplied_lane[2] ^= ((lane[4] >> 3) & 0xff)
-    multiplied_lane[4] ^= ((lane[6] << 3) & 0xff)
-    multiplied_lane[5] ^= ((lane[3] << 2) & 0xff)
+    def _multiply(x):
+        return ordered(
+            reduce(xor, (mj[i](xi) for i, xi in enumerate(ordered(x))))
+            for mj in m
+        )
 
-    return multiplied_lane
+    return _multiply
 
 
 def _multiply_MR2(lane):
@@ -181,7 +192,7 @@ ALPHAS = (
     _multiplication(M),
     _multiplication(M2),
     _multiplication(M3),
-    _multiply_MR,
+    _multiplication(MR, reverse=False),
     _multiply_MR2,
     _multiply_MR3
 )