Huh?

If it was uninicialized, wouldn't the compiler catch it ?

Not necessarily, especially since I don't think it compiles with -Wall by default. Here's some more info from the latest CVS:

sblaster.c line 344:

1static void GenerateDMASound(Bitu size) {
2        Bitu read;Bitu done=0;Bitu i=0;
3        if (sb.dma.left<=sb.dma.min) {
4                size=sb.dma.left;
5        }
6        switch (sb.dma.mode) {

The code cyberwalker posted is inside that switch block. Also, in case anyone suggests that maybe a reference or pointer is being passed, here is the function prototype for AddSamples_s16:

1./hardware/mixer.cpp:void MixerChannel::AddSamples_s16(Bitu len,Bit16s * data) {

Finally, I don't know how Bitu is defined for all platforms, but a grep shows the following for MSVC++:

1./platform/visualc/config.h:typedef unsigned int                Bitu;

Translation: I think cyberwalker is correct.

Function should initialise "read" variable by calling
read=sb.dma.chan->Read(... );
Obviously, that part is missing in case of DSP_DMA_16_ALIASED.
Certainly a bug (because "read" is local non-static variable).