pcm/Export: DSD_U32 quarters the sample rate

DSD_U32 packs four bytes instead of one large "sample", thus the
sample rate is one quarter of the input sample rate.  This fixes a
rather critical DSD_U32 playback problem.

NEWS

@@ -1,6 +1,8 @@
 ver 0.20.2 (not yet released)
 * decoder
   - flac: add options "probesize" and "analyzeduration"
+* output
+  - alsa: fix the DSD_U32 sample rate
 
 ver 0.20.1 (2017/01/09)
 * input

src/pcm/PcmExport.cxx

@@ -101,12 +101,24 @@ PcmExport::GetFrameSize(const AudioFormat &audio_format) const
 unsigned
 PcmExport::Params::CalcOutputSampleRate(unsigned sample_rate) const
 {
+#ifdef ENABLE_DSD
+	if (dsd_u32)
+		/* DSD_U32 combines four 8-bit "samples" in one 32-bit
+		   "sample" */
+		sample_rate /= 4;
+#endif
+
 	return sample_rate;
 }
 
 unsigned
 PcmExport::Params::CalcInputSampleRate(unsigned sample_rate) const
 {
+#ifdef ENABLE_DSD
+	if (dsd_u32)
+		sample_rate *= 4;
+#endif
+
 	return sample_rate;
 }
 

test/test_pcm_export.cxx

@@ -146,6 +146,9 @@ PcmExportTest::TestDsdU32()
 	PcmExport::Params params;
 	params.dsd_u32 = true;
 
+	CPPUNIT_ASSERT_EQUAL(params.CalcOutputSampleRate(705600u), 176400u);
+	CPPUNIT_ASSERT_EQUAL(params.CalcInputSampleRate(176400u), 705600u);
+
 	PcmExport e;
 	e.Open(SampleFormat::DSD, 2, params);