Reduce allocations during readNativeFrames, leading to ~15-20% performance improvement

Makefile

@@ -31,3 +31,10 @@ release:
 	tar -zcvf ${BINARY}-linux-amd64.tar.gz ${BINARY}-linux-amd64; \
 	tar -zcvf ${BINARY}-darwin-amd64.tar.gz ${BINARY}-darwin-amd64; \
 	zip -r ${BINARY}-windows-amd64.exe.zip ${BINARY}-windows-amd64.exe;
+
+bench-diff:
+	go test -bench . -count 5 > bench_current.txt
+	git checkout main
+	go test -bench . -count 5 > bench_main.txt
+	benchstat bench_main.txt bench_current.txt
+	git checkout -

read.go

@@ -223,30 +223,30 @@ func readNativeFrames(d dicomio.Reader, parsedData *Dataset, fc chan<- *frame.Fr
 				Data:          make([][]int, int(pixelsPerFrame)),
 			},
 		}
+		buf := make([]int, int(pixelsPerFrame)*samplesPerPixel)
 		for pixel := 0; pixel < int(pixelsPerFrame); pixel++ {
-			currentPixel := make([]int, samplesPerPixel)
 			for value := 0; value < samplesPerPixel; value++ {
 				if bitsAllocated == 8 {
 					val, err := d.ReadUInt8()
 					if err != nil {
 						return nil, bytesRead, err
 					}
-					currentPixel[value] = int(val)
+					buf[(pixel*samplesPerPixel)+value] = int(val)
 				} else if bitsAllocated == 16 {
 					val, err := d.ReadUInt16()
 					if err != nil {
 						return nil, bytesRead, err
 					}
-					currentPixel[value] = int(val)
+					buf[(pixel*samplesPerPixel)+value] = int(val)
 				} else if bitsAllocated == 32 {
 					val, err := d.ReadUInt32()
 					if err != nil {
 						return nil, bytesRead, err
 					}
-					currentPixel[value] = int(val)
+					buf[(pixel*samplesPerPixel)+value] = int(val)
 				}
 			}
-			currentFrame.NativeData.Data[pixel] = currentPixel
+			currentFrame.NativeData.Data[pixel] = buf[pixel*samplesPerPixel : (pixel+1)*samplesPerPixel]
 		}
 		image.Frames[frameIdx] = currentFrame
 		if fc != nil {

read_test.go

@@ -282,7 +282,7 @@ func TestReadNativeFrames(t *testing.T) {
 				t.Errorf("TestReadNativeFrames(%v): did not get expected error. got: %v, want: %v", tc.data, err, tc.expectedError)
 			}
 
-			if diff := cmp.Diff(pixelData, tc.expectedPixelData); diff != "" {
+			if diff := cmp.Diff(tc.expectedPixelData, pixelData); diff != "" {
 				t.Errorf("TestReadNativeFrames(%v): unexpected diff: %v", tc.data, diff)
 			}
 		})