Bug in PCM shift in G722

[nanang]

There are some issues:

• Clipping detector (to stop shifting). The clip detector in the G722 decoder kicked in immediately when the decoding started, and that it seemed to be due to negative signal levels being fed into the clip detector. The current implementation of the G722 decoder returns values in the range [-16384, 16383]. The way the current clip detector is constructed it will always detect clipping on negative values because of the bit representation of negative values, i.e: MSB is always 1 in two's complement.
• Simple shifting in encoding and decoding, due to bit representation of negative values, simple right/left bits shift may result in unexpected value, e.g: left shifting a positive value may get a negative value, right shifting a negative value will result in a positive value.

This ticket will fix the bugs in clipping detector and in encoding/decoding. Also update clipping detector so the shifting will be reduced step by step after a potential clipping is detected, instead of stopped immediately as in current implementation.

Thanks to Martin Navne for the report and the patch.

[nanang]

In 6064:

Re #2228: Fixed bugs in PCM shifting in G722 codec.

[nanang]

In 6065:

Re #2228: Also updated PCM shifting in G722.1.