local commit

utils.py

@@ -0,0 +1,66 @@
+def int_to_bytes(i: int, b_len: int) -> bytes:
+    """
+    Convert an non-negative int to big-endian unsigned bytes.
+    :param i: The non-negative int.
+    :param b_len: The length of bytes converted into.
+    :return: The bytes.
+    """
+    return i.to_bytes(length=b_len, byteorder='big', signed=False)
+
+
+def bytes_to_int(b: bytes) -> int:
+    """
+    Convert bytes to a big-endian unsigned int.
+    :param b: The bytes to be converted.
+    :return: The int.
+    """
+    return int.from_bytes(bytes=b, byteorder='big', signed=False)
+
+
+def cal_checksum(part: bytes = b'', payload: bytes = b'') -> bytes:
+    """
+    Calculate the checksum for content of segment.
+    :param part: data before checksum
+    :param payload: data after checksum
+    :return: The checksum. The length of checksum is 2 bytes.
+    """
+
+    even_sum = 0x0
+    odd_sum = 0x0
+
+    info = part + payload
+
+    for i in range(len(info)):
+        b = info[i]
+        if i % 2:
+            odd_sum += b
+            odd_sum %= 256
+        else:
+            even_sum += b
+            even_sum %= 256
+
+    even_sum = int_to_bytes(((256 - even_sum) % 256), 1)
+    odd_sum = int_to_bytes(((256 - odd_sum) % 256), 1)
+    return odd_sum + even_sum
+
+
+def judge_checksum(content: bytes) -> bool:
+    """
+    Judge if the checksum is right or not.
+    :param content: the content of segment
+    :return: A bool
+    """
+
+    even_sum = 0x0
+    odd_sum = 0x0
+
+    for i in range(len(content)):
+        b = content[i]
+        if i % 2:
+            odd_sum += b
+            odd_sum %= 256
+        else:
+            even_sum += b
+            even_sum %= 256
+
+    return even_sum == 0 and odd_sum == 0