Fix integer underflow/unsigned wrapping.

The number of xrun fragments to skip is added once to ctx->jack_xruns but
then subtracted multiple times (once for each stream) from the same variable.
This causes the unsigned int to "underflow" and wrap around.

- Use unsigned int in all calculations instead of mixing un/signed.
- Remove erroneous and useless subtraction logic
- Replace for loop by simple multiplication
- Remove unneeded casts to float

src/cubeb_jack.cpp

@@ -290,9 +290,9 @@ cbjack_xrun_callback(void * arg)
   cubeb * ctx = (cubeb *)arg;
 
   float delay = api_jack_get_xrun_delayed_usecs(ctx->jack_client);
-  int fragments = (int)ceilf( ((delay / 1000000.0) * ctx->jack_sample_rate )
-                             / (float)(ctx->jack_buffer_size) );
-  ctx->jack_xruns += fragments;
+  float fragments = ceilf(((delay / 1000000.0) * ctx->jack_sample_rate) / ctx->jack_buffer_size);
+
+  ctx->jack_xruns += (unsigned int)fragments;
   return 0;
 }
 
@@ -332,9 +332,11 @@ static int
 cbjack_process(jack_nframes_t nframes, void * arg)
 {
   cubeb * ctx = (cubeb *)arg;
-  int t_jack_xruns = ctx->jack_xruns;
+  unsigned int t_jack_xruns = ctx->jack_xruns;
   int i;
 
+  ctx->jack_xruns = 0;
+
   for (int j = 0; j < MAX_STREAMS; j++) {
     cubeb_stream *stm = &ctx->streams[j];
     float *bufs_out[stm->out_params.channels];
@@ -344,10 +346,7 @@ cbjack_process(jack_nframes_t nframes, void * arg)
       continue;
 
     // handle xruns by skipping audio that should have been played
-    for (i = 0; i < t_jack_xruns; i++) {
-        stm->position += ctx->fragment_size * stm->ratio;
-    }
-    ctx->jack_xruns -= t_jack_xruns;
+    stm->position += t_jack_xruns * ctx->fragment_size * stm->ratio;
 
     if (!stm->ports_ready)
       continue;