Only mix whole stereo frames in SB 16-bit DMA modekc/sb-dma-1

Thanks to co-authors:
 - @Brandon Roberts for catching this and testing.
 - @Antti Peltola and and @Burrito78 for media procurement
   to assist in reproduction.

In alphabetic order:

Co-authored-by: Antti Peltola <antti.peltola@kolumbus.fi>
Co-authored-by: Brandon Roberts <brandon@bxroberts.org>
Co-authored-by: Burrito78 <Burrito78@users.noreply.github.com>

2 files changed, 25 insertions, 20 deletions

diff --git a/.clang-format b/.clang-format
index d94f112cd..88de09553 100644
--- a/.clang-format
+++ b/.clang-format
@@ -20,7 +20,7 @@ TabWidth: 8
 IndentWidth: 8
 ContinuationIndentWidth: 8
 
-ColumnLimit: 80
+ColumnLimit: 120
 
 # C/C++ Language specifics
 #
diff --git a/src/hardware/sblaster.cpp b/src/hardware/sblaster.cpp
index 09ba53d46..2a568e2ae 100644
--- a/src/hardware/sblaster.cpp
+++ b/src/hardware/sblaster.cpp
@@ -785,30 +785,35 @@ static void PlayDMATransfer(uint32_t bytes_requested)
 			bytes_read = ReadDMA16(bytes_to_read, sb.dma.remain_size);
 			samples = bytes_read / dma16_to_sample_divisor + sb.dma.remain_size;
 			frames = check_cast<uint16_t>(samples / channels);
+
+			if (frames) {
+				// Only add whole frames when in stereo DMA mode, or
 #if defined(WORDS_BIGENDIAN)
-			if (sb.dma.sign) {
-				sb.chan->AddSamples_s16_nonnative(frames,
-				             maybe_silence(samples, sb.dma.buf.b16));
-			} else {
-				sb.chan->AddSamples_s16u_nonnative(frames,
-				             maybe_silence(samples,
-				                           reinterpret_cast<uint16_t *>(sb.dma.buf.b16)));
-			}
+				if (sb.dma.sign) {
+					sb.chan->AddSamples_s16_nonnative(frames,
+					            maybe_silence(samples, sb.dma.buf.b16));
+				} else {
+					sb.chan->AddSamples_s16u_nonnative(frames,
+					            maybe_silence(samples, reinterpret_cast<uint16_t *>(sb.dma.buf.b16)));
+				}
 #else
-			if (sb.dma.sign) {
-				sb.chan->AddSamples_s16(frames,
-				             maybe_silence(samples, sb.dma.buf.b16));
-			} else {
-				sb.chan->AddSamples_s16u(frames,
-				             maybe_silence(samples,
-				                           reinterpret_cast<uint16_t *>(sb.dma.buf.b16)));
-			}
+				if (sb.dma.sign) {
+					sb.chan->AddSamples_s16(frames,
+					            maybe_silence(samples, sb.dma.buf.b16));
+				} else {
+					sb.chan->AddSamples_s16u(frames,
+					            maybe_silence(samples, reinterpret_cast<uint16_t *>(sb.dma.buf.b16)));
+				}
 #endif
-			if (samples & 1) {
+			}
+			else if (samples & 1) {
+				// Carry over the dangling sample into the next round, or
 				sb.dma.remain_size = 1;
 				sb.dma.buf.b16[0] = sb.dma.buf.b16[samples - 1];
-			} else {
-			 sb.dma.remain_size=0;
+			}
+			 else {
+				// The DMA transfer is done
+				sb.dma.remain_size = 0;
 			}
 		} else { // 16-bit mono
 			bytes_read = ReadDMA16(bytes_to_read);