CInt not working as expected in .Net MF

Question

I've got something pretty noddy to cross-fade the colour of an RGB led and I'm having problems getting the desired values.

I've stripped this example down to a bare minimum but Start, End and Steps will all be variable...

This should linearly increment R (UInt) from 0 to 255 in 100 steps. I'm not too worried about precision here so I don't really care if it rounds properly or just does a Floor/Ceiling

    Dim Start As UInteger = 0
    Dim [End] As UInteger = 255
    Dim Steps = 100

    For x = 1 To Steps
        Dim Temp = ([End] - Start) / Steps * x + Start
        Dim R = CUInt(Temp)

        Debug.Print(x.ToString & ": Temp: " & Temp.ToString & ", R:" & R.ToString)
        LedR.SetPulse(255, R)
        Threading.Thread.Sleep(20)
    Next

This Outputs:

1: Temp: 2.5500, R:196608
2: Temp: 5.1000, R:327680
3: Temp: 7.6500, R:524288
4: Temp: 10.2000, R:655360
5: Temp: 12.7499, R:851968
...
95: Temp: 242.2488, R:15859712
96: Temp: 244.7988, R:16056320
97: Temp: 247.3488, R:16187392
98: Temp: 249.8988, R:16384000
99: Temp: 252.4488, R:16515072
100: Temp: 254.9988, R:16711680

As you can see, the Temp variable is pretty-much correct, allowing for some slight imprecision but I can't see what the correlation is with R.

It's possible that CUint is simply reading the bits for Temp and treating the Double as a UInt - but if so, how do I get it to convert it correctly?

(Incidentally, this is running on a netduino), .Net Micro Framework 4.2

Edit: Tests requested below:

    Dim Test As Integer = 2
    Debug.Print(Test.ToString)
    Debug.Print(CInt(Test).ToString)
    Debug.Print(CUInt(Test).ToString)

    2
    2
    2

    Dim Test As Double = 2.5
    Debug.Print(Test.ToString)
    Debug.Print(CInt(Test).ToString)
    Debug.Print(CUInt(Test).ToString)

    2.5000
    131072
    131072

Using the following code...

    For x = 0 To Steps
        Dim Temp As Long = ([End] - Start) \ Steps * x + Start
        Dim R = CType(Temp, UInteger)

        Debug.Print(x.ToString & ": Temp: " & Temp.ToString & ", R:" & R.ToString)
        LedR.SetPulse(255, R)
        Threading.Thread.Sleep(20)
    Next

I get (on the Dim Temp line):

An unhandled exception of type 'System.Exception' occurred in Netduino_VBTest.exe

There's no inner exception but just above it in the output is a first chance exception which I'm guessing is the root cause:

A first chance exception of type 'System.NotImplementedException' occurred in Microsoft.SPOT.Native.dll

Answer 1

Try using Convert.ToUInt32, outlined here: http://msdn.microsoft.com/en-us/library/y3569ft9.aspx

On my .Net 4.0(not Micro) on Windows 7 64bit I am not seeing what you are seeing with CInt/CUInt (mine converts properly). This may be an implementation error in netduino/the Micro Framework... If I had it I would test the above for you.

Answer 2

Whatever is happening I would advise you to avoid UInts as much as you can (I've been there). I would write the code like this:

Dim Start As Integer = 0
Dim [End] As Integer = 255
Dim Steps As Integer = 100

For x As Integer = 1 To Steps
    Dim Temp As Integer = ([End] - Start) \ Steps * x + Start
    LedR.SetPulse(255, CType(Temp,UInteger))
    Threading.Thread.Sleep(20)
Next

I cannot try it because I have not the Vb.Net compiler available and I've wrote the code directly on SO, please forgive me if there are any compilation errors.

Answer 3

Another approach completely different. As the problem looks to be with doubles and conversions we could avoid doubles doing only subtracts:

Dim Start As Integer = 0
Dim [End] As Integer = 255
Dim Increment As Integer = 3
Dim Current as Integer = Start

While Current < End
    Current = Current + Increment
    LedR.SetPulse(255, CType(Current ,UInteger))
    Threading.Thread.Sleep(20)
End While

Quick & Dirty but it works.

Answer 4

How about

Debug.Print(Test.ToString().Split("."c)(0))

I have not worked out any edge-cases, but this worked on a couple of examples I tried. I would not recommend this solution if this will have to be performed in a loop as it will not perform well, but it might be a stop-gap until you can find something better.