mirror of https://bitbucket.org/ausocean/av.git
ADPCM: resructure to encoder and decoder structs
This commit is contained in:
Trek H
parent
7af363a3a4
commit
8f282b1200
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@ -35,9 +35,29 @@ package adpcm
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import (
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"encoding/binary"
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"fmt"
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"io"
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"math"
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)
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// Encoder is used to encode to ADPCM from PCM data.
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// pred and index hold state that persists between calls to encodeSample and calcHead.
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// dest is the output, ie. where the encoded ADPCM data is written to.
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type Encoder struct {
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dest io.Writer
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pred int16
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index int16
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}
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// Decoder is used to decode from ADPCM to PCM data.
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// pred, index, and step hold state that persists between calls to decodeSample.
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// dest is the output, ie. where the decoded PCM data is written to.
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type Decoder struct {
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dest io.Writer
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pred int16
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index int16
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step int16
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}
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// table of index changes (see spec)
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var indexTable = []int16{
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-1, -1, -1, -1, 2, 4, 6, 8,
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@ -60,18 +80,27 @@ var stepTable = []int16{
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32767,
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}
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var (
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encPred int16
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encIndex int16
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decPred int16
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decIndex int16
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decStep int16 = 7
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)
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// NewEncoder retuns a new ADPCM encoder.
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func NewEncoder(dst io.Writer) *Encoder {
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e := Encoder{
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dest: dst,
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}
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return &e
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}
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// NewDecoder retuns a new ADPCM decoder.
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func NewDecoder(dst io.Writer) *Decoder {
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d := Decoder{
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step: stepTable[0],
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dest: dst,
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}
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return &d
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}
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// encodeSample takes a single 16 bit PCM sample and
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// returns a byte of which the last 4 bits are an encoded ADPCM nibble
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func encodeSample(sample int16) byte {
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delta := sample - encPred
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func (e *Encoder) encodeSample(sample int16) byte {
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delta := sample - e.pred
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var nibble byte
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@ -81,7 +110,7 @@ func encodeSample(sample int16) byte {
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delta = -delta
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}
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step := stepTable[encIndex]
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step := stepTable[e.index]
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diff := step >> 3
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var mask byte = 4
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@ -97,25 +126,25 @@ func encodeSample(sample int16) byte {
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// adjust predicted sample based on calculated difference
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if nibble&8 != 0 {
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encPred = capAdd16(encPred, -diff)
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e.pred = capAdd16(e.pred, -diff)
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} else {
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encPred = capAdd16(encPred, diff)
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e.pred = capAdd16(e.pred, diff)
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}
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// check for underflow and overflow
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if encPred < math.MinInt16 {
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encPred = math.MinInt16
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} else if encPred > math.MaxInt16 {
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encPred = math.MaxInt16
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if e.pred < math.MinInt16 {
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e.pred = math.MinInt16
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} else if e.pred > math.MaxInt16 {
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e.pred = math.MaxInt16
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}
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encIndex += indexTable[nibble&7]
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e.index += indexTable[nibble&7]
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// check for underflow and overflow
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if encIndex < 0 {
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encIndex = 0
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} else if encIndex > int16(len(stepTable)-1) {
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encIndex = int16(len(stepTable) - 1)
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if e.index < 0 {
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e.index = 0
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} else if e.index > int16(len(stepTable)-1) {
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e.index = int16(len(stepTable) - 1)
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}
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return nibble
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@ -123,19 +152,19 @@ func encodeSample(sample int16) byte {
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// decodeSample takes a byte, the last 4 bits of which contain a single
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// 4 bit ADPCM nibble, and returns a 16 bit decoded PCM sample
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func decodeSample(nibble byte) int16 {
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func (d *Decoder) decodeSample(nibble byte) int16 {
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// calculate difference
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var diff int16
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if nibble&4 != 0 {
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diff += decStep
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diff += d.step
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}
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if nibble&2 != 0 {
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diff += decStep >> 1
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diff += d.step >> 1
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}
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if nibble&1 != 0 {
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diff += decStep >> 2
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diff += d.step >> 2
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}
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diff += decStep >> 3
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diff += d.step >> 3
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// account for sign bit
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if nibble&8 != 0 {
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@ -143,22 +172,22 @@ func decodeSample(nibble byte) int16 {
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}
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// adjust predicted sample based on calculated difference
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decPred = capAdd16(decPred, diff)
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d.pred = capAdd16(d.pred, diff)
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// adjust index into step size lookup table using nibble
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decIndex += indexTable[nibble]
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d.index += indexTable[nibble]
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// check for overflow and underflow
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if decIndex < 0 {
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decIndex = 0
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} else if decIndex > int16(len(stepTable)-1) {
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decIndex = int16(len(stepTable) - 1)
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if d.index < 0 {
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d.index = 0
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} else if d.index > int16(len(stepTable)-1) {
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d.index = int16(len(stepTable) - 1)
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}
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// find new quantizer step size
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decStep = stepTable[decIndex]
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d.step = stepTable[d.index]
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return decPred
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return d.pred
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}
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// capAdd16 adds two int16s together and caps at max/min int16 instead of overflowing
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@ -174,7 +203,7 @@ func capAdd16(a, b int16) int16 {
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}
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}
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func calcHead(sample []byte) ([]byte, error) {
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func (e *Encoder) calcHead(sample []byte) ([]byte, error) {
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// check that we are given 1 16-bit sample (2 bytes)
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sampSize := 2
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if len(sample) != sampSize {
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@ -182,34 +211,34 @@ func calcHead(sample []byte) ([]byte, error) {
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}
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intSample := int16(binary.LittleEndian.Uint16(sample))
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encodeSample(intSample)
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e.encodeSample(intSample)
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head := make([]byte, 2, 4)
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head[0] = sample[0]
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head[1] = sample[1]
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head = append(head, byte(uint16(encIndex)))
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head = append(head, byte(uint16(e.index)))
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head = append(head, byte(0x00))
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return head, nil
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}
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// EncodeBlock takes a slice of 1010 bytes (505 16-bit PCM samples).
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// It returns a byte slice containing encoded (compressed) ADPCM nibbles (each byte contains two nibbles).
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func EncodeBlock(block []byte) ([]byte, error) {
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func (e *Encoder) EncodeBlock(block []byte) ([]byte, error) {
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bSize := 1010
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if len(block) != bSize {
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return nil, fmt.Errorf("unsupported block size. Given: %v, expected: %v, ie. 505 16-bit PCM samples", len(block), bSize)
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}
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result, err := calcHead(block[0:2])
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result, err := e.calcHead(block[0:2])
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if err != nil {
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return nil, err
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}
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for i := 2; i < len(block); i++ {
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if (i+1)%4 == 0 {
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sample2 := encodeSample(int16(binary.LittleEndian.Uint16(block[i-1 : i+1])))
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sample := encodeSample(int16(binary.LittleEndian.Uint16(block[i+1 : i+3])))
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sample2 := e.encodeSample(int16(binary.LittleEndian.Uint16(block[i-1 : i+1])))
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sample := e.encodeSample(int16(binary.LittleEndian.Uint16(block[i+1 : i+3])))
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result = append(result, byte((sample<<4)|sample2))
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}
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@ -220,16 +249,16 @@ func EncodeBlock(block []byte) ([]byte, error) {
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// DecodeBlock takes a slice of 256 bytes, each byte should contain two ADPCM encoded nibbles.
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// It returns a byte slice containing the resulting decoded (uncompressed) 16-bit PCM samples.
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func DecodeBlock(block []byte) ([]byte, error) {
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func (d *Decoder) DecodeBlock(block []byte) ([]byte, error) {
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bSize := 256
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if len(block) != bSize {
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return nil, fmt.Errorf("unsupported block size. Given: %v, expected: %v", len(block), bSize)
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}
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var result []byte
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decPred = int16(binary.LittleEndian.Uint16(block[0:2]))
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decIndex = int16(block[2])
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decStep = stepTable[decIndex]
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d.pred = int16(binary.LittleEndian.Uint16(block[0:2]))
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d.index = int16(block[2])
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d.step = stepTable[d.index]
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result = append(result, block[0:2]...)
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for i := 4; i < len(block); i++ {
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@ -238,11 +267,11 @@ func DecodeBlock(block []byte) ([]byte, error) {
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firstSample := byte((secondSample << 4) ^ originalSample)
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firstBytes := make([]byte, 2)
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binary.LittleEndian.PutUint16(firstBytes, uint16(decodeSample(firstSample)))
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binary.LittleEndian.PutUint16(firstBytes, uint16(d.decodeSample(firstSample)))
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result = append(result, firstBytes...)
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secondBytes := make([]byte, 2)
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binary.LittleEndian.PutUint16(secondBytes, uint16(decodeSample(secondSample)))
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binary.LittleEndian.PutUint16(secondBytes, uint16(d.decodeSample(secondSample)))
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result = append(result, secondBytes...)
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}
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@ -48,9 +48,10 @@ func TestEncodeBlock(t *testing.T) {
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numBlocks := len(pcm) / inBSize
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outBSize := int(float64(inBSize)/4 + 3.5) // compression is 4:1 and 3.5 bytes of info are added to each block
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comp := make([]byte, 0, outBSize*numBlocks)
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enc := NewEncoder(nil)
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for i := 0; i < numBlocks; i++ {
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block := pcm[inBSize*i : inBSize*(i+1)]
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encBlock, err := EncodeBlock(block)
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encBlock, err := enc.EncodeBlock(block)
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if err != nil {
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log.Fatal(err)
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}
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@ -82,9 +83,10 @@ func TestDecodeBlock(t *testing.T) {
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numBlocks := len(comp) / inBSize
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outBSize := 2 + (inBSize-4)*4 // 2 bytes are copied, 2 are used as block header info, the remaining bytes are decompressed 1:4
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decoded := make([]byte, 0, outBSize*numBlocks)
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dec := NewDecoder(nil)
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for i := 0; i < numBlocks; i++ {
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block := comp[inBSize*i : inBSize*(i+1)]
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decBlock, err := DecodeBlock(block)
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decBlock, err := dec.DecodeBlock(block)
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if err != nil {
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log.Fatal(err)
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}
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