performance improvements

Author: nextroundwinner

.pylintrc

@@ -1,4 +1,7 @@
 [MAIN]
+# make sure tests/ resolves science_mode_4 against the local src/ package
+# instead of whatever version happens to be installed in site-packages
+init-hook='import sys; sys.path.insert(0, "src")'
 max-line-length=150
 max-attributes=15
 max-branches=15

src/science_mode_4/utils/bit_vector.py

@@ -59,9 +59,9 @@ def set_length(self, new_length: int):
         """Set length to new_length, does preserve current data"""
         length_difference = new_length - len(self._data)
         if length_difference > 0:
-            self.extend(BitVector.init_from_int(0, length_difference))
+            self._data.extend([0] * length_difference)
         elif length_difference < 0:
-            self._data = self._data[0:new_length]
+            del self._data[new_length:]
 
 
     def extend(self, value: "BitVector"):
@@ -70,6 +70,23 @@ def extend(self, value: "BitVector"):
             self._data += value._data # pylint: disable=protected-access
 
 
+    def extend_bits_from_int(self, value: int, bit_count: int):
+        """Appends bit_count bits (LSB first) taken from value at the end, without
+        the intermediate zero-fill-then-overwrite of set_length() + __setitem__()"""
+        self._data.extend((value >> x) & 0x1 for x in range(bit_count))
+
+
+    def set_bits_from_int(self, value: int, position: int, bit_count: int):
+        """Sets bit_count bits (LSB first) taken from value starting at position, extending
+        length if necessary. Skips the per-bit bounds/type validation of __setitem__(),
+        which is redundant here because position/bit_count are controlled by the caller"""
+        new_length = max(len(self._data), position + bit_count)
+        self.set_length(new_length)
+        data = self._data
+        for x in range(bit_count):
+            data[position + x] = (value >> x) & 0x1
+
+
     def get_bytes(self) -> bytes:
         """Convert to bytes"""
         result = bytearray()

src/science_mode_4/utils/byte_builder.py

@@ -49,10 +49,7 @@ def set_bit_to_position(self, value: int, bit_position: int, bit_count: int):
         Set bits starting with bit_position and a count of bit_count to value
         This method extends data to make room for value
         """
-        new_length = max(len(self._data), bit_position + bit_count)
-        self._data.set_length(new_length)
-        for x in range(bit_count):
-            self._data[bit_position + x] = (value >> x) & 0x1
+        self._data.set_bits_from_int(value, bit_position, bit_count)
 
 
     def set_bytes_to_position(self, value: bytes, byte_position: int, byte_count: int):
@@ -97,7 +94,4 @@ def __str__(self) -> str:
 
     def _append_byte(self, value: int):
         """Append value at the end of data, value is treated as byte"""
-        start = len(self._data)
-        self._data.set_length(start + 8)
-        for x in range(8):
-            self._data[start + x] = (value >> x) & 0x1
+        self._data.extend_bits_from_int(value, 8)

tests/test_bit_vector.py

@@ -78,6 +78,26 @@ def test_extend_appends_bits_from_other_bitvector():
     assert list(bv) == [1, 0, 1]
 
 
+def test_extend_bits_from_int_appends_lsb_first():
+    bv = BitVector.init_from_int(0b1, 1)
+    bv.extend_bits_from_int(0b101, 3)
+    assert list(bv) == [1, 1, 0, 1]
+    assert bv.get_bytes() == bytes([0b1011])
+
+
+def test_set_bits_from_int_extends_length():
+    bv = BitVector()
+    bv.set_bits_from_int(0b101, 2, 3)
+    assert len(bv) == 5
+    assert list(bv) == [0, 0, 1, 0, 1]
+
+
+def test_set_bits_from_int_overwrites_existing_range():
+    bv = BitVector.init_from_int(0b1111, 4)
+    bv.set_bits_from_int(0b00, 1, 2)
+    assert list(bv) == [1, 0, 0, 1]
+
+
 def test_extend_ignores_non_bitvector_argument():
     # extend() silently does nothing if value is not a BitVector instance
     bv = BitVector.init_from_int(0b1, 1)