[PATCH] winealsa.drv: Optimizations and bug fixes.

[Tomas Carnecky]

There is a bug in how WAVEHDR->reserved is computed, it is possible that 
it is set to a value that can never have been reached (when a WAVEHDR is 
only partially written, then ->reserved is set to 'dwWrittenTotal + 
WAVEHDR->dwBufferSize' when it should be set to 'dwWrittenTotal + 
WAVEHDR->dwBufferSize - dwPartialOffset'). Anyhow, it doesn't make sense 
to update the value after each write as it is fixed as long as the 
header is wwo->lpPlayPtr. The value is now computed only once, when the 
header is prepared for playback.

Only write data if ALSA has space for one period or more available. This 
aims at reducing syscalls (write) with small amounts of data. Given that 
the period usually is very short (10ms), that value could be increased 
even further, to let's say ten periods. But at this time, one period 
seems like a reasonable value as the minimum.

Sleep as long as possible between wakeups. The old code used to wake up 
every 'period' (which is usually 10ms), even if the DSP had been pased 
data for much longer to consume. Now the code checks how much data the 
DSP has ready for playback, and wakes up just before it runs out of 
data. That means when the application has supplied enough data, in big 
enough WAVEHDRs, the driver will be able to sleep for up to ~480ms 
(500ms is the maximum buffer size, plus the code wakes up two periods 
before the DSP runs out of data - to make up for possible delays in 
schedulers etc).

Tested with foobar2000, World of Warcraft, winmm wave test.

CC mlankhorst as he is the current maintainer.

---
  dlls/winealsa.drv/waveout.c |   76 
++++++++++++++++++++++++++++++++----------
  1 files changed, 58 insertions(+), 18 deletions(-)
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