'Based on source found at https://stackoverflow.com/a/23603738, by Juan Pedro Martinez
'
Sub Class_Globals
'decompress table constants
Private aLawDecompressTable() As Short = Array As Short ( -5504, -5248, -6016, -5760, -4480, -4224, -4992, -4736, -7552, -7296, -8064, -7808, -6528, -6272, -7040, -6784, -2752, -2624, -3008, -2880, -2240, -2112, -2496, -2368, -3776, -3648, -4032, -3904, -3264, -3136, -3520, -3392, -22016, -20992, -24064, -23040, -17920, -16896, -19968, -18944, -30208, -29184, -32256, -31232, -26112, -25088, -28160, -27136, -11008, -10496, -12032, -11520, -8960, -8448, -9984, -9472, -15104, -14592, -16128, -15616, -13056, -12544, -14080, -13568, -344, -328, -376, _
-360, -280, -264, -312, -296, -472, -456, -504, -488, -408, -392, -440, -424, -88, -72, -120, -104, -24, -8, -56, -40, -216, -200, -248, -232, -152, -136, -184, -168, -1376, -1312, -1504, -1440, -1120, -1056, -1248, -1184, -1888, -1824, -2016, -1952, -1632, -1568, -1760, -1696, -688, -656, -752, -720, -560, -528, -624, -592, -944, -912, -1008, -976, -816, -784, -880, -848, 5504, 5248, 6016, 5760, 4480, 4224, 4992, 4736, 7552, 7296, 8064, 7808, 6528, 6272, 7040, 6784, 2752, 2624, _
3008, 2880, 2240, 2112, 2496, 2368, 3776, 3648, 4032, 3904, 3264, 3136, 3520, 3392, 22016, 20992, 24064, 23040, 17920, 16896, 19968, 18944, 30208, 29184, 32256, 31232, 26112, 25088, 28160, 27136, 11008, 10496, 12032, 11520, 8960, 8448, 9984, 9472, 15104, 14592, 16128, 15616, 13056, 12544, 14080, 13568, 344, 328, 376, 360, 280, 264, 312, 296, 472, 456, 504, 488, 408, 392, 440, 424, 88, 72, 120, 104, 24, 8, 56, 40, 216, 200, 248, 232, 152, 136, 184, 168, 1376, 1312, 1504, 1440, 1120, _
1056, 1248, 1184, 1888, 1824, 2016, 1952, 1632, 1568, 1760, 1696, 688, 656, 752, 720, 560, 528, 624, 592, 944, 912, 1008, 976, 816, 784, 880, 848 )
Private cClip As Int = 32635
Private aLawCompressTable() As Byte = Array As Byte _
( 1, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7 )
End Sub
'Initializes the object. You can add parameters to this method if needed.
Public Sub Initialize
End Sub
Public Sub Encode(audio() As Byte) As Byte()
Dim length As Int = audio.Length
If length = 0 Then Return Array As Byte()
Dim encoded(length/2) As Byte
Dim offset As Int = 0
Dim count As Int = length / 2
Dim sample As Short = 0
Dim byte1 As Short
Dim byte2 As Short
Dim i As Int
For i = 0 To count - 1
byte1 = Bit.And(audio(offset), 0xff)
offset = offset + 1
byte2 = Bit.ShiftLeft(audio(offset), 8)
offset = offset + 1
sample = Bit.Or( byte1, byte2 )
encoded(i) = linearToALawSample( sample )
Next
Return encoded
End Sub
Private Sub linearToALawSample(sample As Short ) As Byte
Dim sign As Int
Dim exponent As Int
Dim mantissa As Int
Dim s As Int
sign = Bit.And(Bit.ShiftRight(Bit.Not(sample) , 8), 0x80)
If (sign <> 0x80) Then sample = -sample
If ( sample > cClip ) Then sample = cClip
If ( sample >= 256 ) Then
exponent = aLawCompressTable(Bit.And( Bit.ShiftRight(sample , 8 ) , 0x7F))
mantissa = Bit.And( Bit.ShiftRight(sample , ( exponent + 3 ) ) , 0x0F)
s = Bit.Or(Bit.ShiftLeft(exponent,4), mantissa)
Else
s = Bit.ShiftRight(sample,4)
End If
s = Bit.XOR(s , Bit.XOR( sign , 0x55 ))
Return s
End Sub
Public Sub Decode(audio() As Byte) As Byte()
Dim length As Int = audio.Length
If length = 0 Then Return Array As Byte()
Dim decoded(length*2) As Byte
Dim offset As Int = 0
Dim i As Int
Dim s As Short
For i = 0 To length -1
s = aLawDecompressTable(Bit.And(audio(i), 0xff))
decoded(offset) = s
offset = offset + 1
decoded(offset) = Bit.ShiftRight(s, 8)
offset = offset + 1
Next
Return decoded
End Sub