Found with -Wdouble-promotion
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Found with -Wdouble-promotion
Signed-off-by: Rosen Penev <rosenp@gmail.com>

The former was deprecated with C++14.

According to the C++11 and C++17 standards, both files are identical.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Applying software volume to S16 samples means several bits of
precision are lost; at 25% volume, two bits are lost.  Additionally,
dithering adds some noise.

The problem gets worse when you apply the software volume code twice:
for the software mixer volume, and again for the replay gain.  This
loses some more precision and adds even more dithering noise, which
can become audible (see
https://github.com/MusicPlayerDaemon/MPD/issues/542).

By converting everything to 24 bit, we need to shift only two bits to
the right instead of ten, losing nearly no precision, and dithering is
not needed.  Even if the output device is unable to play S24 directly,
we can convert back to S16 with only one stage of dithering.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/542

Prepare for a new mode which may convert to a different sample format
when applying volume, to reduce dithering.

This eliminates some overhead, because the compiler doesn't need to
consider these functions throwing.

While this assert() was useful when we had to track the object's state
manually, there was no practical purpose other than verifying old
code, and it complicates our new C++ code.

Instead of just adding a rectangular random value before shifting back
to the normal scale, use the existing PcmDither library.

Prepare for adding state.

Remove GLib dependency from some headers.

The other audio_format attributes are not used.