Android Question trouble with bc.LongsToBytes

[Hans- Joachim Krahe]

    Dim v(1) As Long
    v(0) = 200
    Dim b() As Byte = bc.LongsToBytes(v)

... how can a byte contain a long?

Dim v3 As Int = b(7) + 256

... this helps, but maybe doesn't care the reason

    Dim v3 As Long = val

    v3 = Bit.UnsignedShiftRight(v3,1)

Bit.UnsignedShiftRight seems to work with long as well, not only with int as declared. Very usefull

 

[Semen Matusovskiy]

In Java a byte represents a value between −128 - 127 (signed).
200 (dec) = 0xC8 (hex).
0xC8 like unsigned is 200, like signed -56 (256 - 200)

 

[Hans- Joachim Krahe]

so it is a java specific thing. Is there any way to keep the result unsigned or does it work by tricks only, wehen i operate bytes and ints? Need it for midi straming...

 

[Semen Matusovskiy]

For typical operations with bytes the sign is not important (for example, reading a file into array of bytes or conversion string to bytes). So tricks are not needed.
Of course, a math can be problematic.
Which operations confuse you ?

 

[Hans- Joachim Krahe]

a long needs to be represented in bytes, but only 7bit per byte, because most significant bit is signal. And it should work fast. So I am unshure, if I prefere binary string operations with substrings or maths.

private Sub midiDeltaFromDez (ticks As Long) As Long
 
private Sub midiDeltaFromDez (ticks As Long) As Long
   
    Dim long1, long2, long3 As Long
    Dim tickStr As String = ticks
    Dim bitstr As String = getBitStr(ticks)
    Dim bitbyte() As Byte =  bitstr.GetBytes("utf8")
    Dim bitbyte2(bitbyte.Length) As Byte
    For i = 0 To bitbyte.Length - 1
        bitbyte2(i) = bitbyte(bitbyte.Length - i - 1)
    Next
   
   
    'If Bit.
    'bc.
    If  ticks < 128 Then
        For i = 0 To 6
            If bitbyte2(i)= 49 Then
                long1 = long1  +  Power( 2,i)
            End If
        Next
       
        ' 1 byte
    else If ticks < 16384 Then
        ' 2 byte
        For i = 0 To 6
            If bitbyte2(i)= 49 Then
                long1 = long1  +  Power( 2,i)
            End If
        Next
        For i = 7 To bitbyte.Length - 1
            If bitbyte2(i)= 49 Then
                long2 = long2  +  Power( 2,i)
            End If
        Next
        'long2 = long2  + 128
       
    Else If ticks < 2097152 Then
        ' 3 byte
        'int1 = 
        For i = 0 To 6
            If bitbyte2(i)= 49 Then
                long1 = long1  +  Power( 2,i)
            End If
        Next
        For i = 7 To 13
            If bitbyte2(i)= 49 Then
                long2 = long2  +  Power( 2,i)
            End If
        Next
    Else
        For i = 0 To 6
            If bitbyte2(i)= 49 Then
                long1 =long1+  Power( 2,i)
            End If
        Next
        For i = 7 To 13
            If bitbyte2(i)= 49 Then
                long2 = long2  +  Power( 2,i)
            End If
        Next
        For i = 7 To 13
            If bitbyte2(i)= 49 Then
                long3 = long3  +  Power( 2,i)
            End If
        Next
       
    End If
   
End Sub
 
End Sub

 

[Semen Matusovskiy]

I don't see dangerous operations with bytes (maybe I lost something).
Comparasion (=48, =49) and moving (bitbyte2(i) = bitbyte(bitbyte.Length - i - 1)) only.

 

[Hans- Joachim Krahe]

Yes, this would be a konservativ solution. The delay could be satisfactory because in fast action, the ticks are short and only needs the smaller algorithm.

 

[Erel]

The correct way to convert a signed byte to an unsigned value:

Sub ToUnsigned(b As Byte) As Int
 Return Bit.And(0xFF, b)
End Sub

 

[DonManfred]

he already know this
https://www.b4x.com/android/forum/threads/no-uinteger-in-b4a-solved.99685/