Decimal-to-Hex Problem?

alfcen

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Longtime User
Working on a wireless BT telescope controller that converts angles (right ascension and declination)
to an 8 digits hex string with two trailing zeros for a telescope to slew towards, say, a star.

B4X:
Sub Deg2Hex(x As Double, y As Double, grid As String) As String
   Dim hexra, hexde As String
   x = Round(x * 46603.378)
   y = Round(y * 46603.378)
   If y < 0 Then y = 16777216 + y
   hexra = Bit.ToHexString(x) & "00000000"
   hexra = hexra.SubString2(0,8).ToUpperCase
   hexde = Bit.ToHexString(y) & "00000000"
   hexde = hexde.SubString2(0,8).ToUpperCase
   Select grid
      Case "eqt"
         Return "r" & hexra & "," & hexde
      Case "azm"
         Return "b" & hexra & "," & hexde      
   End Select
End Sub
The above routine works perfectly for most angles, but around x = 165 it gives wrong results.

The routine is the same as the one I once used with Basic4ppc, employing "hexra=bit.DecToHex(x)" with
no issues at all.

This raises the question whether "Bit.ToHexString" in B4A could contain a bug, such as omission of a leading
zero in a hex string. Or, my choice of conversion to Hex is a wrong one.

Cheers
Robert
 

agraham

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Longtime User
Why is the algorithm taking the left hand side using SubString? Surely that will make, for example, angles of 1 and 16 return very similar results.

I'm sure there is no bug in ToHexString but it never returns a leading zero so if you are expecting an even number of digits you would need to do your own test and add a leading zero if necessary.
 
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alfcen

Well-Known Member
Licensed User
Longtime User
Please ignore my previous reply to your post. I have deleted it.

Rather than digging deeper, I decided to add leading zeros as you suggested,
as, indeed, the scope expects hex strings in even pairs.

Thanks a lot for the trigger.
 
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