Fix encoding of integers

Too many bytes were previously used as plaintext, which made the
computation unnecessarily inefficient. Test cases are added here to
detect future changes in the ordering determined by the seed.

Note: this changes the ordering of integers done by this library for
existing seeds, which could be a breaking change depending on the use case.

Author: bbc2

CHANGELOG.md

@@ -9,6 +9,9 @@ Versioning].
 
 - Drop support for Python 3.7, Python 3.8 and PyPy3.8.
 - Add tests with Python 3.14 and PyPy3.11.
+- Improve performance by reducing the AES plaintext size. Note: this changes the
+  ordering of integers for existing seeds, which may be a breaking change depending
+  on the use case.
 
 ## [1.1.0] - 2022-12-29
 

src/shuffled/crypto.py

@@ -27,7 +27,7 @@ def __init__(self, key: bytes) -> None:
         self._encryptor = cipher.encryptor()
 
     def randomize(self, integer: int) -> int:
-        encoded = integer.to_bytes(128, byteorder="big")
+        encoded = integer.to_bytes(16, byteorder="big")
         encrypted = self._encryptor.update(encoded)
         return int.from_bytes(encrypted, byteorder="big")
 

tests/test_shuffled.py

@@ -13,8 +13,21 @@ def test_normal(self, range_size):
         assert sorted(list(shuffled_range)) == list(range(range_size))
 
     @pytest.mark.parametrize(
-        "seed",
-        (b"", b"\x00", b"\x01"),
+        "seed, expected",
+        (
+            (
+                b"",
+                [4, 5, 6, 1, 2, 7, 8, 3, 10, 11, 13, 9, 16, 17, 12, 15, 18, 19, 14, 0],
+            ),
+            (
+                b"\x00",
+                [13, 14, 17, 7, 3, 15, 16, 6, 2, 5, 9, 12, 18, 10, 1, 19, 4, 0, 8, 11],
+            ),
+            (
+                b"\x01",
+                [11, 0, 9, 5, 6, 10, 19, 4, 13, 14, 8, 16, 17, 18, 15, 12, 1, 2, 7, 3],
+            ),
+        ),
     )
-    def test_seed(self, seed):
-        assert list(Shuffled(20, seed)) == list(Shuffled(20, seed))
+    def test_seed(self, seed, expected):
+        assert list(Shuffled(20, seed)) == expected