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Merge pull request #391 from andlaus/improve_encoding_fallbacks
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improve the fallback code for some undefined encodings in non-strict mode
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@andlaus
andlaus authored Feb 20, 2025
2 parents a2bff12 + bf32e80 commit 1e5f030
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Showing 2 changed files with 98 additions and 42 deletions.
53 changes: 35 additions & 18 deletions odxtools/decodestate.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -103,7 +103,9 @@ def extract_atomic_value(

# Deal with raw byte fields, ...
if base_data_type == DataType.A_BYTEFIELD:
odxassert(base_type_encoding in (None, Encoding.NONE, Encoding.BCD_P, Encoding.BCD_UP))
odxassert(
base_type_encoding in (None, Encoding.NONE, Encoding.BCD_P, Encoding.BCD_UP),
f"Illegal encoding '{base_type_encoding}' for A_BYTEFIELD")

# note that we do not ensure that BCD-encoded byte fields
# only represent "legal" values
Expand Down Expand Up @@ -149,28 +151,19 @@ def extract_atomic_value(
odxraise(f"Illegal encoding ({base_type_encoding}) specified for "
f"{base_data_type.value}")

internal_value = raw_value
if base_type_encoding == Encoding.BCD_P:
internal_value = self.__decode_bcd_p(raw_value)
elif base_type_encoding == Encoding.BCD_UP:
internal_value = self.__decode_bcd_up(raw_value)
else:
internal_value = raw_value

# ... unsigned integers, ...
elif base_data_type == DataType.A_UINT32:
if base_type_encoding == Encoding.BCD_P:
# packed BCD
tmp2 = raw_value
internal_value = 0
factor = 1
while tmp2 > 0:
internal_value += (tmp2 & 0xf) * factor
factor *= 10
tmp2 >>= 4
internal_value = self.__decode_bcd_p(raw_value)
elif base_type_encoding == Encoding.BCD_UP:
# unpacked BCD
tmp2 = raw_value
internal_value = 0
factor = 1
while tmp2 > 0:
internal_value += (tmp2 & 0xf) * factor
factor *= 10
tmp2 >>= 8
internal_value = self.__decode_bcd_up(raw_value)
elif base_type_encoding in (None, Encoding.NONE):
# no encoding
internal_value = raw_value
Expand All @@ -193,3 +186,27 @@ def extract_atomic_value(
self.cursor_bit_position = 0

return internal_value

@staticmethod
def __decode_bcd_p(value: int) -> int:
# packed BCD
result = 0
factor = 1
while value > 0:
result += (value & 0xf) * factor
factor *= 10
value >>= 4

return result

@staticmethod
def __decode_bcd_up(value: int) -> int:
# unpacked BCD
result = 0
factor = 1
while value > 0:
result += (value & 0xf) * factor
factor *= 10
value >>= 8

return result
87 changes: 63 additions & 24 deletions odxtools/encodestate.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -101,17 +101,26 @@ def emplace_atomic_value(
odxraise(f"{internal_value!r} is not a bytefield", EncodeError)
return

odxassert(base_type_encoding in (None, Encoding.NONE, Encoding.BCD_P, Encoding.BCD_UP))
odxassert(
base_type_encoding in (None, Encoding.NONE, Encoding.BCD_P, Encoding.BCD_UP),
f"Illegal encoding '{base_type_encoding}' for A_BYTEFIELD")

# note that we do not ensure that BCD-encoded byte fields
# only represent "legal" values
raw_value = bytes(internal_value)

if 8 * len(raw_value) > bit_length:
odxraise(
f"The value '{internal_value!r}' cannot be encoded using "
f"{bit_length} bits.", EncodeError)
raw_value = raw_value[0:bit_length // 8]

# ... string types, ...
elif base_data_type in (DataType.A_UTF8STRING, DataType.A_ASCIISTRING,
DataType.A_UNICODE2STRING):
if not isinstance(internal_value, str):
odxraise(f"The internal value {internal_value!r} is not a string", EncodeError)
odxraise(f"The internal value '{internal_value!r}' is not a string", EncodeError)
internal_value = str(internal_value)

str_encoding = get_string_encoding(base_data_type, base_type_encoding,
is_highlow_byte_order)
Expand All @@ -122,16 +131,17 @@ def emplace_atomic_value(

if 8 * len(raw_value) > bit_length:
odxraise(
f"The internal representation {raw_value!r} is too large "
f"to be encoded. The maximum number of bytes is {(bit_length + 7)//8}.",
EncodeError)
f"The value '{internal_value!r}' cannot be encoded using "
f"{bit_length} bits.", EncodeError)
raw_value = raw_value[0:bit_length // 8]

# ... signed integers, ...
elif base_data_type == DataType.A_INT32:
if not isinstance(internal_value, int):
odxraise(
f"Internal value must be of integer type, not {type(internal_value).__name__}",
EncodeError)
internal_value = int(internal_value)

if base_type_encoding == Encoding.ONEC:
# one-complement
Expand All @@ -154,34 +164,35 @@ def emplace_atomic_value(
else:
raw_value = (1 << (bit_length - 1)) + abs(internal_value)
else:
odxraise(f"Illegal encoding ({base_type_encoding}) specified for "
f"{base_data_type.value}")
odxraise(
f"Illegal encoding ({base_type_encoding and base_type_encoding.value}) specified for "
f"{base_data_type.value}")

raw_value = internal_value
if base_type_encoding == Encoding.BCD_P:
raw_value = self.__encode_bcd_p(abs(internal_value))
elif base_type_encoding == Encoding.BCD_UP:
raw_value = self.__encode_bcd_up(abs(internal_value))
else:
raw_value = internal_value

if raw_value.bit_length() > bit_length:
odxraise(
f"The value '{internal_value!r}' cannot be encoded using "
f"{bit_length} bits.", EncodeError)
raw_value &= (1 << bit_length) - 1

# ... unsigned integers, ...
elif base_data_type == DataType.A_UINT32:
if not isinstance(internal_value, int) or internal_value < 0:
odxraise(f"Internal value must be a positive integer, not {internal_value!r}")
internal_value = abs(int(internal_value))

if base_type_encoding == Encoding.BCD_P:
# packed BCD
tmp2 = internal_value
raw_value = 0
shift = 0
while tmp2 > 0:
raw_value |= (tmp2 % 10) << shift
shift += 4
tmp2 //= 10
raw_value = self.__encode_bcd_p(internal_value)
elif base_type_encoding == Encoding.BCD_UP:
# unpacked BCD
tmp2 = internal_value
raw_value = 0
shift = 0
while tmp2 > 0:
raw_value |= (tmp2 % 10) << shift
shift += 8
tmp2 //= 10
raw_value = self.__encode_bcd_up(internal_value)
elif base_type_encoding in (None, Encoding.NONE):
# no encoding
raw_value = internal_value
Expand All @@ -191,6 +202,12 @@ def emplace_atomic_value(

raw_value = internal_value

if raw_value.bit_length() > bit_length:
odxraise(
f"The value '{internal_value!r}' cannot be encoded using "
f"{bit_length} bits.", EncodeError)
raw_value &= (1 << bit_length) - 1

# ... and others (floating point values)
else:
odxassert(base_data_type in (DataType.A_FLOAT32, DataType.A_FLOAT64))
Expand All @@ -210,15 +227,15 @@ def emplace_atomic_value(
self.emplace_bytes(b'')
return

char = base_data_type.bitstruct_format_letter
format_char = base_data_type.bitstruct_format_letter
padding = (8 - ((bit_length + self.cursor_bit_position) % 8)) % 8
odxassert((0 <= padding and padding < 8 and
(padding + bit_length + self.cursor_bit_position) % 8 == 0),
f"Incorrect padding {padding}")
left_pad = f"p{padding}" if padding > 0 else ""

# actually encode the value
coded = bitstruct.pack(f"{left_pad}{char}{bit_length}", raw_value)
coded = bitstruct.pack(f"{left_pad}{format_char}{bit_length}", raw_value)

# create the raw mask of used bits for numeric objects
used_mask_raw = used_mask
Expand Down Expand Up @@ -290,3 +307,25 @@ def emplace_bytes(self,
self.used_mask[pos + i] |= obj_used_mask[i]

self.cursor_byte_position += len(new_data)

@staticmethod
def __encode_bcd_p(value: int) -> int:
result = 0
shift = 0
while value > 0:
result |= (value % 10) << shift
shift += 4
value //= 10

return result

@staticmethod
def __encode_bcd_up(value: int) -> int:
result = 0
shift = 0
while value > 0:
result |= (value % 10) << shift
shift += 8
value //= 10

return result

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