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Fix mask calculation to avoid incorrect 0 values caused by compiler optimization

Bastien Nocera requested to merge github/fork/bdutro/master into master

Created by: bdutro

Problem

On my machine, iio-sensor-proxy was returning all 0's for my accelerometer sensor values. It turns out that the bits_used for this sensor is 32, which makes the mask calculation:

*mask = (1 << 32) - 1;

If the compiler interprets the 1 literals as 32-bit ints, it generates undefined behavior depending on compiler version and optimization level. In my case, it optimizes out the shift, so the mask value becomes

*mask = (1) - 1;

With a mask value of 0, iio-sensor-proxy will always return 0 for every axis.

Fix

Explicitly mark the 1 literals as unsigned 64-bit ints so that we never encounter the undefined behavior case.

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