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Change _int_decoder to allow uint32 into smaller types instead of OverflowException #32

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Change _int_decoder to allow uint32 into smaller types instead of OverflowException #32

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11 changes: 7 additions & 4 deletions src/pysparkplug/_datatype.py
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Original file line number Diff line number Diff line change
Expand Up @@ -122,10 +122,13 @@ def _int_encoder(value: int, bits: int) -> int:


def _int_decoder(value: int, bits: int) -> int:
max_val: int = 2**bits
if not 0 <= value < max_val:
raise OverflowError(f"Int{bits} overflow with value {value}")
return value - (max_val if value >= 2 ** (bits - 1) else 0)
mask = (1 << bits) - 1 # e.g. 0xFFFF for 16 bits
value &= mask # drop any higher bits
sign_bit = 1 << (bits - 1) # e.g. 0x8000 for 16 bits
if value & sign_bit: # if sign bit is set
value -= 1 << bits

return value


def _encode_numeric_array(values: Sequence[float], format_char: str) -> bytes:
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12 changes: 8 additions & 4 deletions test/unit_tests/test_datatype.py
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Original file line number Diff line number Diff line change
Expand Up @@ -134,11 +134,15 @@ def test_integer_encoding(self):
decoded, value, f"Failed to encode/decode {value} with {dtype}"
)

def test_decoder_errors(self) -> None:
with self.assertRaises(OverflowError):
# too large
DataType.INT8.decode(2**9)
def test_decoding_sign_extended_values(self):
value = -87
signExtendedValue = (
value & 0xFFFFFFFF # packed into uint32 for Google Protobuf
)
decoded = DataType.INT16.decode(signExtendedValue)
self.assertEqual(decoded, value)

def test_decoder_errors(self) -> None:
with self.assertRaises(ValueError):
# not enough bytes
DataType.INT16_ARRAY.decode(b"\x00")
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