C/cpp Checksum function to Xojo.

General
1

I have a function that needs to be converted to Xojo code.

unsigned char CheckSum(unsigned char *uBuff, unsigned char uBuffLen) {
  unsigned char i,uSum=0; 

  for(i=0;i<uBuffLen;i++) {
    uSum = uSum + uBuff[i]; 
  }

  uSum = (~uSum) + 1;
  
return uSum; 
}

Anyone quicker than me about this? I have made a prototype but it doesn’t seem to work. Hope you can do better.

2

Not sure if this is what you need or not

function CheckSum(uBuff() as uInt8, ubuffLen as UInt8) as Uint8
dim i as uInt8
dim uSum as integer // not uint8 as you don't know the range required
for i=0 to uBuffLen-1
usum=usum+ubuff(i)
next i
usum=(usum and &HFF) // strip off only the last 8 bits
// usum=(-usum)+1 //  this doesn't make sense as a UInt cannot be negative
return uSum
end function
3

using uSum as Uint8 will loop the numbers as requested
this is a version using a memory block as src

Function checksum(m as MemoryBlock) As UInt8 dim uSum,i,ubufferLen as UInt8 ubufferLen=m.Size-1 for i =0 to ubufferLen uSum=uSum+m.UInt8Value(i) next Return (not uSum)+1 End Function

4

the ~ is bitwise not (flips all bits) not just making it negative

5

It’s used for a serial and http protocol.

Should i be using BinaryStream to create a packet (from Uint8’s) then return a string using a nil encoding?
i’m in a bit of a hang because i tried the new framework but it doesn’t seem to help me it keeps crashing with unknown reason.

Perhaps it’s the encoding. But i’m not sure.

6

Does UInt8 overflow gracefully???
if not then this won’t work

  for i =0 to ubufferLen
    uSum=uSum+m.UInt8Value(i)
  next
7

Uint8 should overflow correctly

8

Yes they do :wink:

9

It works. the function is now:

Function Checksum(Data As String = "") As UInt8
  Dim uSum As UInt8 = 0
  
  If Data <> "" Then
    
    For i As integer = 0 to Len( Data )
      
      uSum = uSum + Asc( Mid( Data, i, i+1 ) )
      
    Next
    
  End If
  
  uSum = (Not uSum) + 1
  
  Return uSum
End Function
10

Thanks all for your input. I made it so it works for my cause.