Audio: Google RTC audio processing: Mix all channels in mockup

With this change e.g. in all 2ch case all output channels are
mixed with matching microphone and reference channels. It helps
with testing to hear and see that the mockup works.

The mix is done for matching microphone, reference and output
channels indices. With e.g. less reference channels, the remaining
output channels are passed directly from microphone.

The mixed samples are saturated to avoid nasty sounding overflows.

Signed-off-by: Lionel Koenig <lionelk@google.com>
Signed-off-by: Seppo Ingalsuo <seppo.ingalsuo@linux.intel.com>

src/audio/google/google_rtc_audio_processing_mock.c

@@ -10,6 +10,8 @@
 #include <string.h>
 #include <stdint.h>
 
+#include <sof/audio/format.h>
+#include <sof/math/numbers.h>
 #include <rtos/alloc.h>
 #include "ipc/topology.h"
 
@@ -145,11 +147,23 @@ int GoogleRtcAudioProcessingProcessCapture_int16(GoogleRtcAudioProcessingState *
 	int16_t *ref = state->aec_reference;
 	int16_t *mic = (int16_t *) src;
 	int16_t *out = dest;
-	int n;
+	int n, io, im, ir;
 
+	/* Mix input and reference channels to output. The matching channels numbers
+	 * are mixed. If e.g. microphone and output channels count is 4, and reference
+	 * has 2 channels, output channels 3 and 4 are copy of microphone channels 3 and 4,
+	 * and output channels 1 and 2 are sum of microphone and reference.
+	 */
 	memset(dest, 0, sizeof(int16_t) * state->num_output_channels * state->num_frames);
 	for (n = 0; n < state->num_frames; ++n) {
-		*out = *mic + *ref;
+		im = 0;
+		ir = 0;
+		for (io = 0; io < state->num_output_channels; io++) {
+			out[io] = sat_int16(
+				(im < state->num_capture_channels ? (int32_t)mic[im++] : 0) +
+				(ir < state->num_aec_reference_channels ? (int32_t)ref[ir++] : 0));
+		}
+
 		ref += state->num_aec_reference_channels;
 		out += state->num_output_channels;
 		mic += state->num_capture_channels;