When using this code:
(int8_t)tmp102_read_temp_x100() / 100
Only the first value is casted into a int8_t type.
tmp102_read_temp_x100() returns the temperature in Celcius * 100. Most of
the time this value will be lower than -2^7 and higher than 2^7 (+/- 1.27°C).
The cast is not needed but a comment about this implicit cast has been added.
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