From e60429a83eb0f90003030d2193ce78519ad54259 Mon Sep 17 00:00:00 2001
From: Drew Weymouth <dweymouth@gmail.com>
Date: Sat, 19 Jul 2025 10:31:15 -0700
Subject: [PATCH] Reuse tmp buffers in calls to PCMBuffer

---
 decoder.go | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/decoder.go b/decoder.go
index 66f2bb7..316d8a6 100644
--- a/decoder.go
+++ b/decoder.go
@@ -42,6 +42,9 @@ type Decoder struct {
 	PCMChunk *riff.Chunk
 	// Metadata for the current file
 	Metadata *Metadata
+
+	readBuf   []byte
+	sampleBuf [4]byte
 }
 
 // NewDecoder creates a decoder for the passed wav reader.
@@ -250,8 +253,6 @@ func (d *Decoder) FullPCMBuffer() (*audio.IntBuffer, error) {
 	}
 
 	buf := &audio.IntBuffer{Data: make([]int, 4096), Format: format, SourceBitDepth: int(d.BitDepth)}
-	bytesPerSample := (d.BitDepth-1)/8 + 1
-	sampleBufData := make([]byte, bytesPerSample)
 	decodeF, err := sampleDecodeFunc(int(d.BitDepth))
 	if err != nil {
 		return nil, fmt.Errorf("could not get sample decode func %w", err)
@@ -259,7 +260,7 @@ func (d *Decoder) FullPCMBuffer() (*audio.IntBuffer, error) {
 
 	i := 0
 	for err == nil {
-		buf.Data[i], err = decodeF(d.PCMChunk, sampleBufData)
+		buf.Data[i], err = decodeF(d.PCMChunk, d.sampleBuf[:])
 		if err != nil {
 			break
 		}
@@ -309,9 +310,9 @@ func (d *Decoder) PCMBuffer(buf *audio.IntBuffer) (n int, err error) {
 	// populate a file buffer to avoid multiple very small reads
 	// we need to cap the buffer size to not be bigger than the pcm chunk.
 	size := len(buf.Data) * bPerSample
-	tmpBuf := make([]byte, size)
+	d.ensureReadBufSize(size)
 	var m int
-	m, err = d.PCMChunk.R.Read(tmpBuf)
+	m, err = d.PCMChunk.R.Read(d.readBuf)
 	if err != nil {
 		if errors.Is(err, io.EOF) {
 			return m, nil
@@ -321,8 +322,7 @@ func (d *Decoder) PCMBuffer(buf *audio.IntBuffer) (n int, err error) {
 	if m == 0 {
 		return m, nil
 	}
-	bufR := bytes.NewReader(tmpBuf[:m])
-	sampleBuf := make([]byte, bPerSample, bPerSample)
+	bufR := bytes.NewReader(d.readBuf[:m])
 	var misaligned bool
 	if m%bPerSample > 0 {
 		misaligned = true
@@ -331,7 +331,7 @@ func (d *Decoder) PCMBuffer(buf *audio.IntBuffer) (n int, err error) {
 	// Note that we populate the buffer even if the
 	// size of the buffer doesn't fit an even number of frames.
 	for n = 0; n < len(buf.Data); n++ {
-		buf.Data[n], err = decodeF(bufR, sampleBuf)
+		buf.Data[n], err = decodeF(bufR, d.sampleBuf[:])
 		if err != nil {
 			// the last sample isn't a full sample but just padding.
 			if misaligned {
@@ -409,6 +409,12 @@ func (d *Decoder) String() string {
 	return d.parser.String()
 }
 
+func (d *Decoder) ensureReadBufSize(size int) {
+	if len(d.readBuf) < size {
+		d.readBuf = make([]byte, size)
+	}
+}
+
 // readHeaders is safe to call multiple times
 func (d *Decoder) readHeaders() error {
 	if d == nil || d.NumChans > 0 {