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Reuse tmp buffers in calls to PCMBuffer to avoid allocations #44

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Reuse tmp buffers in calls to PCMBuffer to avoid allocations #44

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22 changes: 14 additions & 8 deletions decoder.go
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Original file line number Diff line number Diff line change
Expand Up @@ -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.
Expand Down Expand Up @@ -250,16 +253,14 @@ 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)
}

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
}
Expand Down Expand Up @@ -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
Expand All @@ -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
Expand All @@ -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 {
Expand Down Expand Up @@ -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 {
Expand Down