mirror of https://bitbucket.org/ausocean/av.git
ADPCM: Encoding and decoding blocks fully functional.
This commit is contained in:
Trek H
parent
a8d4e0db6a
commit
f03c8052d6
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package adpcm
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import (
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"encoding/binary"
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"fmt"
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"math"
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)
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// table of index changes
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var indexTable = []int16{
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-1, -1, -1, -1, 2, 4, 6, 8,
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-1, -1, -1, -1, 2, 4, 6, 8,
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}
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// quantize step size table
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var stepTable = []int16{
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7, 8, 9, 10, 11, 12, 13, 14,
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16, 17, 19, 21, 23, 25, 28, 31,
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34, 37, 41, 45, 50, 55, 60, 66,
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73, 80, 88, 97, 107, 118, 130, 143,
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157, 173, 190, 209, 230, 253, 279, 307,
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337, 371, 408, 449, 494, 544, 598, 658,
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724, 796, 876, 963, 1060, 1166, 1282, 1411,
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1552, 1707, 1878, 2066, 2272, 2499, 2749, 3024,
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3327, 3660, 4026, 4428, 4871, 5358, 5894, 6484,
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7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,
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15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794,
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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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pCount int
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pNum = 8
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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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// find difference from predicted sample
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delta := sample - encPred
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// set sign bit and find absolute value of difference
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var nibble byte
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if delta < 0 {
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nibble = 8
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delta = -delta
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}
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step := stepTable[encIndex]
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diff := step >> 3
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var mask byte = 4
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// quantize delta down to four bits
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for i := 0; i < 3; i++ {
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if delta > step {
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nibble |= mask
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delta -= step
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diff += step
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}
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mask >>= 1
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step >>= 1
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}
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// adjust predicted sample based on calculated difference
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if nibble&8 != 0 {
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encPred -= diff
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} else {
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encPred += 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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}
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encIndex += 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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}
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return nibble
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}
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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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// compute predicted sample estimate (decPred):
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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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}
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if nibble&2 != 0 {
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diff += decStep >> 1
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}
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if nibble&1 != 0 {
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diff += decStep >> 2
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}
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diff += decStep >> 3
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// account for sign bit
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if nibble&8 != 0 {
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diff = -diff
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}
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// adjust predicted sample based on calculated difference
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decPred += diff
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// check for overflow and underflow
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if decPred > math.MaxInt16 {
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decPred = math.MaxInt16
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} else if decPred < math.MinInt16 {
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decPred = math.MinInt16
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}
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// compute new step size:
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// adjust index into step size lookup table using nibble
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decIndex += 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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}
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// find new quantizer step size
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decStep = stepTable[decIndex]
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return decPred
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}
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func calcHead(sample []byte) ([]byte, error) {
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if len(sample) != 2 {
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return nil, fmt.Errorf("length of given byte array is: %v, expected: 2", len(sample))
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}
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intSample := int16(binary.LittleEndian.Uint16(sample))
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// if pCount < pNum {
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// fmt.Println("calcHead enc", intSample)
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// fmt.Println(encIndex, encPred)
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// }
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EncodeSample(intSample)
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head := make([]byte, 2)
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head[0] = sample[0]
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head[1] = sample[1]
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// if pCount < pNum {
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// fmt.Println("after calcHead enc")
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// fmt.Println(encIndex, encPred)
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// }
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head = append(head, byte(uint16(encIndex)))
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head = append(head, byte(0x00))
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return head, nil
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}
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func EncodeBlock(block []byte) ([]byte, error) {
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if len(block) != 1010 {
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return nil, fmt.Errorf("unsupported block size. Given: %v, expected: 1010, ie. 505 16-bit PCM samples", len(block))
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}
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result, err := 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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// var intsample int16
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// if pCount < pNum {
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// fmt.Println(block[2], block[3])
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// fmt.Println("first enc", block[i-1:i+1])
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// fmt.Println(encIndex, encPred)
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// }
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sample2 := EncodeSample(int16(binary.LittleEndian.Uint16(block[i-1 : i+1])))
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// if pCount < pNum {
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// intsample = int16(binary.LittleEndian.Uint16(block[i+1 : i+3]))
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// fmt.Println("second enc", int16(intsample))
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// fmt.Println(encIndex, encPred)
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// }
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sample := EncodeSample(int16(binary.LittleEndian.Uint16(block[i+1 : i+3])))
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// if pCount < pNum {
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// fmt.Println("after enc")
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// fmt.Println(encIndex, encPred)
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// fmt.Println()
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// }
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result = append(result, byte((sample<<4)|sample2))
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pCount++
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}
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}
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return result, nil
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}
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func DecodeBlock(block []byte) ([]byte, error) {
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if len(block) != 256 {
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return nil, fmt.Errorf("unsupported block size. Given: %v, expected: 256", len(block))
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}
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if pCount < pNum {
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fmt.Println("pre dec", block[0:8])
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fmt.Println(decIndex, decPred, decStep)
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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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result = append(result, block[0:2]...)
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for i := 4; i < len(block); i++ {
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originalSample := block[i]
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secondSample := byte(originalSample >> 4)
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firstSample := byte((secondSample << 4) ^ originalSample)
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if pCount < pNum {
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fmt.Println("first dec", firstSample, originalSample, len(block))
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fmt.Println(decIndex, decPred, decStep)
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}
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firstBytes := make([]byte, 2)
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binary.LittleEndian.PutUint16(firstBytes, uint16(DecodeSample(firstSample)))
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result = append(result, firstBytes...)
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if pCount < pNum {
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fmt.Println("second dec", secondSample)
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fmt.Println(decIndex, decPred, decStep)
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fmt.Println()
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}
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secondBytes := make([]byte, 2)
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binary.LittleEndian.PutUint16(secondBytes, uint16(DecodeSample(secondSample)))
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result = append(result, secondBytes...)
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pCount++
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}
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return result, nil
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}
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