pcm_export: implement 24 to 32 bit conversion

For 32 bit DSD-over-USB support.

4 files changed, 26 insertions, 4 deletions

diff --git a/src/output/alsa_output_plugin.c b/src/output/alsa_output_plugin.c
index 00ddbfb5c..c9dd1ee1b 100644
--- a/src/output/alsa_output_plugin.c
+++ b/src/output/alsa_output_plugin.c
@@ -634,7 +634,7 @@ alsa_setup_or_dsd(struct alsa_data *ad, struct audio_format *audio_format,
 
 	pcm_export_open(&ad->export,
 			audio_format->format, audio_format->channels,
-			dsd_usb, packed, reverse_endian);
+			dsd_usb, false, packed, reverse_endian);
 	return true;
 }
 
diff --git a/src/output/oss_output_plugin.c b/src/output/oss_output_plugin.c
index 85bdc37dc..f59ee3b92 100644
--- a/src/output/oss_output_plugin.c
+++ b/src/output/oss_output_plugin.c
@@ -540,7 +540,7 @@ oss_probe_sample_format(int fd, enum sample_format sample_format,
 	*oss_format_r = oss_format;
 
 #ifdef AFMT_S24_PACKED
-	pcm_export_open(export, sample_format, 0, false,
+	pcm_export_open(export, sample_format, 0, false, false,
 			oss_format == AFMT_S24_PACKED,
 			oss_format == AFMT_S24_PACKED &&
 			G_BYTE_ORDER != G_LITTLE_ENDIAN);
diff --git a/src/pcm_export.c b/src/pcm_export.c
index 66ed6d351..dbd9f2e8e 100644
--- a/src/pcm_export.c
+++ b/src/pcm_export.c
@@ -41,7 +41,7 @@ void pcm_export_deinit(struct pcm_export_state *state)
 void
 pcm_export_open(struct pcm_export_state *state,
 		enum sample_format sample_format, unsigned channels,
-		bool dsd_usb, bool pack, bool reverse_endian)
+		bool dsd_usb, bool shift8, bool pack, bool reverse_endian)
 {
 	assert(audio_valid_sample_format(sample_format));
 	assert(!dsd_usb || audio_valid_channel_count(channels));
@@ -53,8 +53,11 @@ pcm_export_open(struct pcm_export_state *state,
 		   samples are stuffed inside fake 24 bit samples */
 		sample_format = SAMPLE_FORMAT_S24_P32;
 
+	state->shift8 = shift8 && sample_format == SAMPLE_FORMAT_S24_P32;
 	state->pack24 = pack && (sample_format == SAMPLE_FORMAT_S24_P32 || sample_format == SAMPLE_FORMAT_DSD_OVER_USB);
 
+	assert(!state->shift8 || !state->pack24);
+
 	state->reverse_endian = 0;
 	if (reverse_endian) {
 		size_t sample_size = state->pack24
@@ -90,8 +93,21 @@ pcm_export(struct pcm_export_state *state, const void *data, size_t size,
 
 		data = dest;
 		size = dest_size;
+	} else if (state->shift8) {
+		assert(size % 4 == 0);
+
+		const uint8_t *src8 = data, *src_end8 = src8 + size;
+		const uint32_t *src = (const uint32_t *)src8;
+		const uint32_t *const src_end = (const uint32_t *)src_end8;
+
+		uint32_t *dest = pcm_buffer_get(&state->pack_buffer, size);
+		data = dest;
+
+		while (src < src_end)
+			*dest++ = *src++ << 8;
 	}
 
+
 	if (state->reverse_endian > 0) {
 		assert(state->reverse_endian >= 2);
 
diff --git a/src/pcm_export.h b/src/pcm_export.h
index c132c7169..418dcdfa3 100644
--- a/src/pcm_export.h
+++ b/src/pcm_export.h
@@ -69,6 +69,12 @@ struct pcm_export_state {
 	bool dsd_usb;
 
 	/**
+	 * Convert (padded) 24 bit samples to 32 bit by shifting 8
+	 * bits to the left?
+	 */
+	bool shift8;
+
+	/**
 	 * Pack 24 bit samples?
 	 */
 	bool pack24;
@@ -106,7 +112,7 @@ pcm_export_deinit(struct pcm_export_state *state);
 void
 pcm_export_open(struct pcm_export_state *state,
 		enum sample_format sample_format, unsigned channels,
-		bool dsd_usb, bool pack, bool reverse_endian);
+		bool dsd_usb, bool shift8, bool pack, bool reverse_endian);
 
 /**
  * Export a PCM buffer.