Determine what bits are high in Integer?

Question

I have a 32-bit integer that I am reading from a motion controller. The integer represents error bits that are set in the controller. I have nine (9) errors, or error bits that can be set high at any one time. In any case, one, or all nine bits can be set at the same time, or any combination in between. Identifying that there is an error is easy obviously, since if the value of the Integer is > 0, then we know there's an error. The difficult part it appears is how can I identify which errors (bits) are set, since there is a myriad of different combinations of bits that could be set high at any one time. I started trying to mask (If Integer > 0 And < 96, then checkbox1.checked = True), etc, but this seems like a nightmare since there are so many combinations. Is there a more efficient way to do this? The bits in the integer that can be set high are: (2, 6, 7, 8, 11, 12, 13, 14, and 21)

Answer 1

A clean way is to define an enum with all your errors associated with their bit.

Public Enum MotionControlerErrors As Integer

  NoMorePower = 1 << 2
  Explosion = 1 << 6 
  SomeOtherError = 1 << 7

   ...

End Enum

You could then use it this way to build a list of bit out of your error :

Function BuildMaskList( ErrorResult As integer ) As List(Of Boolean)
  Dim ResultList As New List( Of Boolean) 
  For Each err In MotionControlerErrors
    ResultList.Add ( (err AND ErrorResult) = err )
  End For
  Return ResultList
End Function

Answer 2

You could use bit operations and a counter to figure out which bits are set, something like:

int[] set_bits = new int[9]
int currentBit = 0
for (int i = 0; i < 32; i++)
{
    firstBit = errorNumber & 0x1   //firstBit >= 1 only if it is set
    if (firstBit >= 1)
    {
       set_bits[currentBit] = 1
       currentBit++
    }

    errorNumber = errorNumber >> 1   //shift the bits down by one for the next bit
}

Then you can operate depending on which index of set_bits is set. Sorry I am unfamiliar with VB but I'm positive VB has something similar if not exactly like this. I think that the general concept of bit shifting and binary operators are what you are looking for to solve this.

Here are logical bitwise operators ('and'-ing numbers together and arithmatic operations (bit shifting numbers)

Answer 3

You want a bitwise AND operation, with appropriate masks:

if error bit 6:
00111010 <-- input from your controller
00100000 <-- mask value for error bit 6
--------
00100000 <-- output bits are set only where the input matches the mask


if no error bit 6:
00011010 <-- input from your controller
00100000 <-- mask value for error bit 6
--------
00000000 <-- output bits are set only where the input matches the mask

I haven't got VB.Net handy to check, but https://stackoverflow.com/a/4046492/478656 suggests that the AND operator will work. (32 is the integer value of just bit 6 being set)

if (errorValue AND 32) = 32 Then Checkbox1.checked = True

You would probably benefit from having an interpretation layer, telling you what the bits mean (e.g. bit 6 is 'motor burnt out', and then setting a boolean saying 'motorBurntOutFlag = true', so you aren't playing guess-the-magic-numbers.

e.g. https://stackoverflow.com/a/666254/478656

Enum controllerErrors as Integer
    powerFail = 2
    incompatibleCommand = 32
    ...
End Enum

if (errorValue AND controllerErrors.powerFail) > 0 Then
    'code
end if