ADPCM: fixed spacing and overflow check

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

@@ -1,3 +1,30 @@
+/*
+NAME
+  decode-pcm.go
+
+DESCRIPTION
+  See Readme.md
+
+AUTHOR
+  Trek Hopton <trek@ausocean.org>
+
+LICENSE
+  decode-pcm.go is Copyright (C) 2018 the Australian Ocean Lab (AusOcean)
+
+  It is free software: you can redistribute it and/or modify them
+  under the terms of the GNU General Public License as published by the
+  Free Software Foundation, either version 3 of the License, or (at your
+  option) any later version.
+
+  It is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with revid in gpl.txt.  If not, see [GNU licenses](http://www.gnu.org/licenses).
+*/
+
 package main
 
 import (
@@ -16,11 +43,13 @@ func main() {
 	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
 	comp, err := ioutil.ReadFile(inPath)
 	if err != nil {
 		panic(err)
 	}
+
 	//decode adpcm
 	var decoded []byte
 	start := 0
@@ -35,6 +64,7 @@ func main() {
 			start = i + 1
 		}
 	}
+
 	// save pcm to file
 	err = ioutil.WriteFile(outPath, decoded, 0644)
 	if err != nil {

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

@@ -1,3 +1,30 @@
+/*
+NAME
+  encode-pcm.go
+
+DESCRIPTION
+  See Readme.md
+
+AUTHOR
+  Trek Hopton <trek@ausocean.org>
+
+LICENSE
+  encode-pcm.go is Copyright (C) 2018 the Australian Ocean Lab (AusOcean)
+
+  It is free software: you can redistribute it and/or modify them
+  under the terms of the GNU General Public License as published by the
+  Free Software Foundation, either version 3 of the License, or (at your
+  option) any later version.
+
+  It is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with revid in gpl.txt.  If not, see [GNU licenses](http://www.gnu.org/licenses).
+*/
+
 package main
 
 import (
@@ -13,6 +40,7 @@ func main() {
 	flag.StringVar(&inPath, "in", "data.pcm", "file path of input data")
 	flag.StringVar(&adpcmPath, "out", "encoded.adpcm", "file path of output")
 	flag.Parse()
+
 	//read pcm
 	pcm, err := ioutil.ReadFile(inPath)
 	if err != nil {
@@ -35,6 +63,7 @@ func main() {
 			start = i + 1
 		}
 	}
+
 	// save adpcm to file
 	err = ioutil.WriteFile(adpcmPath, comp, 0644)
 	if err != nil {

stream/adpcm/adpcm.go

@@ -1,3 +1,35 @@
+/*
+NAME
+  adpcm.go
+
+DESCRIPTION
+  See Readme.md
+
+AUTHOR
+  Trek Hopton <trek@ausocean.org>
+
+LICENSE
+  adpcm.go is Copyright (C) 2018 the Australian Ocean Lab (AusOcean)
+
+  It is free software: you can redistribute it and/or modify them
+  under the terms of the GNU General Public License as published by the
+  Free Software Foundation, either version 3 of the License, or (at your
+  option) any later version.
+
+  It is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with revid in gpl.txt.  If not, see [GNU licenses](http://www.gnu.org/licenses).
+*/
+
+/*
+	Original IMA/DVI ADPCM specification: (http://www.cs.columbia.edu/~hgs/audio/dvi/IMA_ADPCM.pdf).
+	Reference algorithms for ADPCM compression and decompression are in part 6.
+*/
+
 package adpcm
 
 import (
@@ -6,13 +38,13 @@ import (
 	"math"
 )
 
-// table of index changes
+// table of index changes (see spec)
 var indexTable = []int16{
 	-1, -1, -1, -1, 2, 4, 6, 8,
 	-1, -1, -1, -1, 2, 4, 6, 8,
 }
 
-// quantize step size table
+// quantize step size table (see spec)
 var stepTable = []int16{
 	7, 8, 9, 10, 11, 12, 13, 14,
 	16, 17, 19, 21, 23, 25, 28, 31,
@@ -39,7 +71,6 @@ var (
 // encodeSample takes a single 16 bit PCM sample and
 // returns a byte of which the last 4 bits are an encoded ADPCM nibble
 func encodeSample(sample int16) byte {
-
 	delta := sample - encPred
 
 	var nibble byte
@@ -93,9 +124,6 @@ func encodeSample(sample int16) byte {
 // decodeSample takes a byte, the last 4 bits of which contain a single
 // 4 bit ADPCM nibble, and returns a 16 bit decoded PCM sample
 func decodeSample(nibble byte) int16 {
-
-	// compute predicted sample estimate (decPred):
-
 	// calculate difference
 	var diff int16
 	if nibble&4 != 0 {
@@ -108,30 +136,37 @@ func decodeSample(nibble byte) int16 {
 		diff += decStep >> 2
 	}
 	diff += decStep >> 3
+
 	// account for sign bit
 	if nibble&8 != 0 {
 		diff = -diff
 	}
-	// adjust predicted sample based on calculated difference
-	decPred += diff
 
-	// check for overflow and underflow
-	if decPred > math.MaxInt16 {
+	// adjust predicted sample based on calculated difference, check for overflow
+	if diff > 0 {
+		if decPred > math.MaxInt16-diff {
 			decPred = math.MaxInt16
-	} else if decPred < math.MinInt16 {
-		decPred = math.MinInt16
+		} else {
+			decPred += diff
+		}
+	} else {
+		if decPred < math.MaxInt16-diff {
+			decPred = math.MaxInt16
+		} else {
+			decPred += diff
+		}
 	}
-
-	// compute new step size:
 
 	// adjust index into step size lookup table using nibble
 	decIndex += indexTable[nibble]
+
 	// check for overflow and underflow
 	if decIndex < 0 {
 		decIndex = 0
 	} else if decIndex > int16(len(stepTable)-1) {
 		decIndex = int16(len(stepTable) - 1)
 	}
+
 	// find new quantizer step size
 	decStep = stepTable[decIndex]
 
@@ -139,7 +174,6 @@ func decodeSample(nibble byte) int16 {
 }
 
 func calcHead(sample []byte) ([]byte, error) {
-
 	// check that we are given 1 16-bit sample (2 bytes)
 	sampSize := 2
 	if len(sample) != sampSize {
@@ -161,7 +195,6 @@ func calcHead(sample []byte) ([]byte, error) {
 // EncodeBlock takes a slice of 1010 bytes (505 16-bit PCM samples).
 // It returns a byte slice containing encoded (compressed) ADPCM nibbles (each byte contains two nibbles).
 func EncodeBlock(block []byte) ([]byte, error) {
-
 	bSize := 1010
 	if len(block) != bSize {
 		return nil, fmt.Errorf("unsupported block size. Given: %v, expected: %v, ie. 505 16-bit PCM samples", len(block), bSize)
@@ -187,7 +220,6 @@ func EncodeBlock(block []byte) ([]byte, error) {
 // DecodeBlock takes a slice of 256 bytes, each byte should contain two ADPCM encoded nibbles.
 // It returns a byte slice containing the resulting decoded (uncompressed) 16-bit PCM samples.
 func DecodeBlock(block []byte) ([]byte, error) {
-
 	bSize := 256
 	if len(block) != bSize {
 		return nil, fmt.Errorf("unsupported block size. Given: %v, expected: %v", len(block), bSize)
@@ -211,7 +243,6 @@ func DecodeBlock(block []byte) ([]byte, error) {
 		secondBytes := make([]byte, 2)
 		binary.LittleEndian.PutUint16(secondBytes, uint16(decodeSample(secondSample)))
 		result = append(result, secondBytes...)
-
 	}
 
 	return result, nil

stream/adpcm/adpcm_test.go

@@ -1,3 +1,30 @@
+/*
+NAME
+  adpcm_test.go
+
+DESCRIPTION
+  See Readme.md
+
+AUTHOR
+  Trek Hopton <trek@ausocean.org>
+
+LICENSE
+  adpcm_test.go is Copyright (C) 2018 the Australian Ocean Lab (AusOcean)
+
+  It is free software: you can redistribute it and/or modify them
+  under the terms of the GNU General Public License as published by the
+  Free Software Foundation, either version 3 of the License, or (at your
+  option) any later version.
+
+  It is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with revid in gpl.txt.  If not, see [GNU licenses](http://www.gnu.org/licenses).
+*/
+
 package adpcm
 
 import (
@@ -14,6 +41,7 @@ func TestEncodeBlock(t *testing.T) {
 	if err != nil {
 		t.Errorf("Unable to read input PCM file: %v", err)
 	}
+
 	//encode adpcm
 	var comp []byte
 	start := 0
@@ -23,13 +51,13 @@ func TestEncodeBlock(t *testing.T) {
 
 			encBlock, err := EncodeBlock(block)
 			if err != nil {
-				//todo: use correct logging of error
 				t.Errorf("Unable to encode block: %v", err)
 			}
 			comp = append(comp, encBlock...)
 			start = i + 1
 		}
 	}
+
 	//read expected adpcm file
 	exp, err := ioutil.ReadFile("../../../test/test-data/av/output/encoded-voice.adpcm")
 	if err != nil {
@@ -49,6 +77,7 @@ func TestDecodeBlock(t *testing.T) {
 	if err != nil {
 		t.Errorf("Unable to read input ADPCM file: %v", err)
 	}
+
 	//decode adpcm
 	var decoded []byte
 	start := 0
@@ -63,6 +92,7 @@ func TestDecodeBlock(t *testing.T) {
 			start = i + 1
 		}
 	}
+
 	//read expected pcm file
 	exp, err := ioutil.ReadFile("../../../test/test-data/av/output/decoded-voice.pcm")
 	if err != nil {