添加 checksum 实现

Author: TakWolf

src/sfnttools/internal/checksum.py

@@ -0,0 +1,14 @@
+from typing import Final
+
+CHECKSUM_MASK: Final = 0xFFFFFFFF
+
+
+def calculate_checksum(data: bytes) -> int:
+    checksum = 0
+    for i in range(0, len(data), 4):
+        chunk = data[i:i + 4]
+        if len(chunk) < 4:
+            chunk += b'\x00' * (4 - len(chunk))
+        checksum += int.from_bytes(chunk, 'big', signed=False)
+    checksum &= CHECKSUM_MASK
+    return checksum

tests/test_checksum.py

@@ -0,0 +1,6 @@
+from sfnttools.internal.checksum import calculate_checksum
+
+
+def test_calculate_checksum():
+    assert calculate_checksum(b'abcd') == 1633837924
+    assert calculate_checksum(b'abcdxyz') == 3655064932