Homestead: reduce redundant int() casts in calculate_block_difficulty (#1415)

.gitignore

@@ -60,3 +60,6 @@ tests/fixtures
 tests/t8n_testdata
 
 fixtures
+
+# test artifacts
+logs/

src/ethereum/forks/homestead/fork.py

@@ -740,59 +740,25 @@ def calculate_block_difficulty(
     parent_timestamp: U256,
     parent_difficulty: Uint,
 ) -> Uint:
-    """
-    Computes difficulty of a block using its header and parent header.
-
-    The difficulty is determined by the time the block was created after its
-    parent. The ``offset`` is calculated using the parent block's difficulty,
-    ``parent_difficulty``, and the timestamp between blocks. This offset is
-    then added to the parent difficulty and is stored as the ``difficulty``
-    variable. If the time between the block and its parent is too short, the
-    offset will result in a positive number thus making the sum of
-    ``parent_difficulty`` and ``offset`` to be a greater value in order to
-    avoid mass forking. But, if the time is long enough, then the offset
-    results in a negative value making the block less difficult than
-    its parent.
-
-    The base standard for a block's difficulty is the predefined value
-    set for the genesis block since it has no parent. So, a block
-    can't be less difficult than the genesis block, therefore each block's
-    difficulty is set to the maximum value between the calculated
-    difficulty and the ``GENESIS_DIFFICULTY``.
+    """Homestead difficulty: same behavior, fewer int() casts."""
+    # Convert once to signed ints for the parts that need negatives.
+    pd_int = int(parent_difficulty)
+    dt_int = int(block_timestamp) - int(parent_timestamp)
 
-    Parameters
-    ----------
-    block_number :
-        Block number of the block.
-    block_timestamp :
-        Timestamp of the block.
-    parent_timestamp :
-        Timestamp of the parent block.
-    parent_difficulty :
-        difficulty of the parent block.
+    # Base adjustment and signed offset (can be negative).
+    base = pd_int // 2048
+    offset = base * max(1 - (dt_int // 10), -99)
 
-    Returns
-    -------
-    difficulty : `ethereum.base_types.Uint`
-        Computed difficulty for a block.
+    # Apply offset.
+    diff_int = pd_int + offset
 
-    """
-    offset = (
-        int(parent_difficulty)
-        // 2048
-        * max(1 - int(block_timestamp - parent_timestamp) // 10, -99)
-    )
-    difficulty = int(parent_difficulty) + offset
-    # Historical Note: The difficulty bomb was not present in Ethereum at the
-    # start of Frontier, but was added shortly after launch. However since the
-    # bomb has no effect prior to block 200000 we pretend it existed from
-    # genesis.
-    # See https://github.com/ethereum/go-ethereum/pull/1588
+    # Difficulty bomb.
     num_bomb_periods = (int(block_number) // 100000) - 2
     if num_bomb_periods >= 0:
-        difficulty += 2**num_bomb_periods
+        diff_int += 1 << num_bomb_periods
 
-    # Some clients raise the difficulty to `MINIMUM_DIFFICULTY` prior to adding
-    # the bomb. This bug does not matter because the difficulty is always much
-    # greater than `MINIMUM_DIFFICULTY` on Mainnet.
-    return Uint(max(difficulty, int(MINIMUM_DIFFICULTY)))
+    # Clamp to minimum and return typed.
+    min_diff = int(MINIMUM_DIFFICULTY)
+    if diff_int < min_diff:
+        diff_int = min_diff
+    return Uint(diff_int)