kontron / python-ipmi / 37296559577

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sdr: fix conversion of sensor value to raw value

convert_sensor_value_to_raw() did not compute the inverse of the
conversion formula y = (M * x + B * 10^K1) * 10^K2. The offset B was
subtracted after the division by M instead of before:

  raw = value * 10^-K2 / M - B * 10^K1        (wrong)
  raw = (value * 10^-K2 - B * 10^K1) / M      (correct)

This led to wrong raw values for all sensors with B != 0, e.g. for a
3.3V sensor with M=16, B=163, K2=-3 the value 3.843V was converted to
the raw value 77 instead of 230.

Additionally the encoding of 1's and 2's complement values now depends
on the sign of the raw value instead of the sign of the given value,
because with an offset B these can differ. A negative raw value for an
unsigned sensor now raises a ValueError instead of returning a negative
raw value.

The existing tests only used B=0 where both formulas give the same
result. Add tests with an offset.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Heiko Thiery <heiko.thiery@gmail.com>

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