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"
@@ -39,22 +40,23 @@ 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 {
+	// 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 {
@@ -63,11 +65,11 @@ func main() {
 		decoded = append(decoded, decBlock...)
 		start = i + 1
 	}
-	}
 
 	// save pcm to file
 	err = ioutil.WriteFile(outPath, decoded, 0644)
 	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
@@ -46,15 +49,15 @@ 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 {
+	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)
@@ -62,11 +65,11 @@ func main() {
 		comp = append(comp, encBlock...)
 		start = i + 1
 	}
-	}
 
 	// save adpcm to file
 	err = ioutil.WriteFile(adpcmPath, comp, 0644)
 	if err != nil {
 		panic(err)
 	}
+	fmt.Println("Encoded and wrote", len(comp), "bytes to file", adpcmPath)
 }

stream/adpcm/adpcm_test.go

@@ -44,9 +44,8 @@ func TestEncodeBlock(t *testing.T) {
 
 	//encode adpcm
 	var comp []byte
-	start := 0
-	for i := 0; i < len(pcm); i++ {
-		if i%1010 == 1009 {
+	bSize := 1010
+	for i, start := bSize-1, 0; i < len(pcm); i += bSize {
 		block := pcm[start : i+1]
 
 		encBlock, err := EncodeBlock(block)
@@ -56,7 +55,6 @@ func TestEncodeBlock(t *testing.T) {
 		comp = append(comp, encBlock...)
 		start = i + 1
 	}
-	}
 
 	//read expected adpcm file
 	exp, err := ioutil.ReadFile("../../../test/test-data/av/output/encoded-voice.adpcm")
@@ -80,9 +78,8 @@ func TestDecodeBlock(t *testing.T) {
 
 	//decode adpcm
 	var decoded []byte
-	start := 0
-	for i := 0; i < len(comp); i++ {
-		if i%256 == 255 {
+	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 {
@@ -91,7 +88,6 @@ func TestDecodeBlock(t *testing.T) {
 		decoded = append(decoded, decBlock...)
 		start = i + 1
 	}
-	}
 
 	//read expected pcm file
 	exp, err := ioutil.ReadFile("../../../test/test-data/av/output/decoded-voice.pcm")