ADPCM: pre-allocating memory for entire known length of output byte slice

cmd/adpcm/decode-pcm/decode-pcm.go

@@ -29,6 +29,7 @@ package main
 
 import (
 	"flag"
+	"fmt"
 	"io/ioutil"
 
 	"bitbucket.org/ausocean/av/stream/adpcm"
@@ -39,30 +40,30 @@ import (
 func main() {
 	var inPath string
 	var outPath string
-
 	flag.StringVar(&inPath, "in", "encoded.adpcm", "file path of input")
 	flag.StringVar(&outPath, "out", "decoded.pcm", "file path of output data")
 	flag.Parse()
 
-	//read adpcm
+	// read adpcm
 	comp, err := ioutil.ReadFile(inPath)
 	if err != nil {
 		panic(err)
 	}
+	fmt.Println("Read", len(comp), "bytes from file", inPath)
 
-	//decode adpcm
-	var decoded []byte
-	start := 0
-	for i := 0; i < len(comp); i++ {
-		if i%256 == 255 {
-			block := comp[start : i+1]
-			decBlock, err := adpcm.DecodeBlock(block)
-			if err != nil {
-				panic(err)
-			}
-			decoded = append(decoded, decBlock...)
-			start = i + 1
+	// decode adpcm
+	inBSize := 256
+	numBlocks := int(len(comp) / inBSize)
+	outBSize := 2 + (inBSize-4)*4 // 2 bytes are copied, 2 are used as block header info, the remaining bytes are decompressed 1:4
+	decoded := make([]byte, 0, outBSize*numBlocks)
+	for i, start := inBSize-1, 0; i < len(comp); i += inBSize {
+		block := comp[start : i+1]
+		decBlock, err := adpcm.DecodeBlock(block)
+		if err != nil {
+			panic(err)
 		}
+		decoded = append(decoded, decBlock...)
+		start = i + 1
 	}
 
 	// save pcm to file
@@ -70,4 +71,5 @@ func main() {
 	if err != nil {
 		panic(err)
 	}
+	fmt.Println("Decoded and wrote", len(decoded), "bytes to file", outPath)
 }

cmd/adpcm/encode-pcm/encode-pcm.go

@@ -29,11 +29,14 @@ package main
 
 import (
 	"flag"
+	"fmt"
 	"io/ioutil"
 
 	"bitbucket.org/ausocean/av/stream/adpcm"
 )
 
+// This program accepts an input pcm file and outputs an encoded adpcm file.
+// Input and output file names can be specified as arguments.
 func main() {
 	var inPath string
 	var adpcmPath string
@@ -46,22 +49,21 @@ func main() {
 	if err != nil {
 		panic(err)
 	}
+	fmt.Println("Read", len(pcm), "bytes from file", inPath)
 
 	//encode adpcm
-	var comp []byte
-	start := 0
-	bSize := 1010
-	for i := 0; i < len(pcm); i++ {
-		if i%bSize == bSize-1 {
-			block := pcm[start : i+1]
-
-			encBlock, err := adpcm.EncodeBlock(block)
-			if err != nil {
-				panic(err)
-			}
-			comp = append(comp, encBlock...)
-			start = i + 1
+	inBSize := 1010
+	numBlocks := int(len(pcm) / inBSize)
+	outBSize := int(float32(inBSize/4) + float32(3.5)) // compression is 4:1 and 3.5 bytes of info are added to each block
+	comp := make([]byte, 0, outBSize*numBlocks)
+	for i, start := inBSize-1, 0; i < len(pcm); i += inBSize {
+		block := pcm[start : i+1]
+		encBlock, err := adpcm.EncodeBlock(block)
+		if err != nil {
+			panic(err)
 		}
+		comp = append(comp, encBlock...)
+		start = i + 1
 	}
 
 	// save adpcm to file
@@ -69,4 +71,5 @@ func main() {
 	if err != nil {
 		panic(err)
 	}
+	fmt.Println("Encoded and wrote", len(comp), "bytes to file", adpcmPath)
 }

stream/adpcm/adpcm_test.go

@@ -44,18 +44,16 @@ func TestEncodeBlock(t *testing.T) {
 
 	//encode adpcm
 	var comp []byte
-	start := 0
-	for i := 0; i < len(pcm); i++ {
-		if i%1010 == 1009 {
-			block := pcm[start : i+1]
+	bSize := 1010
+	for i, start := bSize-1, 0; i < len(pcm); i += bSize {
+		block := pcm[start : i+1]
 
-			encBlock, err := EncodeBlock(block)
-			if err != nil {
-				t.Errorf("Unable to encode block: %v", err)
-			}
-			comp = append(comp, encBlock...)
-			start = i + 1
+		encBlock, err := EncodeBlock(block)
+		if err != nil {
+			t.Errorf("Unable to encode block: %v", err)
 		}
+		comp = append(comp, encBlock...)
+		start = i + 1
 	}
 
 	//read expected adpcm file
@@ -80,17 +78,15 @@ func TestDecodeBlock(t *testing.T) {
 
 	//decode adpcm
 	var decoded []byte
-	start := 0
-	for i := 0; i < len(comp); i++ {
-		if i%256 == 255 {
-			block := comp[start : i+1]
-			decBlock, err := DecodeBlock(block)
-			if err != nil {
-				t.Errorf("Unable to decode block: %v", err)
-			}
-			decoded = append(decoded, decBlock...)
-			start = i + 1
+	bSize := 256
+	for i, start := bSize-1, 0; i < len(comp); i += bSize {
+		block := comp[start : i+1]
+		decBlock, err := DecodeBlock(block)
+		if err != nil {
+			t.Errorf("Unable to decode block: %v", err)
 		}
+		decoded = append(decoded, decBlock...)
+		start = i + 1
 	}
 
 	//read expected pcm file