image/jpeg: make writeDQT do fewer array copies.

R=rsc, r
CC=golang-dev
https://golang.org/cl/4536069

diff --git a/src/pkg/image/jpeg/writer.go b/src/pkg/image/jpeg/writer.go
index 4a861b39519509eea12d6ab8b0a91bdf999f6890..c23372f0ec5a6bb3763318ee78304c6c87070fcb 100644 (file)
--- a/src/pkg/image/jpeg/writer.go
+++ b/src/pkg/image/jpeg/writer.go
@@ -302,14 +302,11 @@ func (e *encoder) writeMarkerHeader(marker uint8, markerlen int) {
 
 // writeDQT writes the Define Quantization Table marker.
 func (e *encoder) writeDQT() {
-       markerlen := 2
-       for _, q := range e.quant {
-               markerlen += 1 + len(q)
-       }
+       markerlen := 2 + int(nQuantIndex)*(1+blockSize)
        e.writeMarkerHeader(dqtMarker, markerlen)
-       for i, q := range e.quant {
+       for i := range e.quant {
                e.writeByte(uint8(i))
-               e.write(q[:])
+               e.write(e.quant[i][:])
        }
 }