Big Integer handling in Blitz Basic 2D?

i had a quick try. this works but only for positive values. i got stuck then.

i think the best way is to write a dll to receive a string from b+, do the maths function as 64-bit values, and return the result as a string.

Graphics 640,480,0,2

value2$="100000020"
value1$="3000"
result$=AddLongString(value1$,value2$)

Print "value1="+value1
Print "value2="+value2
Print "result="+result+" ("+(100000020+3000)+")"
WaitKey
End

Function AddLongString$(val1$,val2$)

 Local val1hi,val1lo,val2hi,val2lo,reshi$,reslo$,i,pad$
 If (Len(val1$)>9) val1hi=Int(Left(val1$,Len(val1$)-9))
 val1lo=Int(Right(val1$,9))
 If (Len(val2$)>9) val2hi=Int(Left(val2$,Len(val2$)-9))
 val2lo=Int(Right(val2$,9))
 If (val1hi+val2hi<>0) reshi$=val1hi+val2hi
 If (val1lo+val2lo<>0) reslo$=val1lo+val2lo
 For i=1 To 9-Len(reslo$)
  pad$=pad$+"0" 
 Next
 Return reshi$+pad$+reslo$

End Function