Sum of digits

BlitzMax Forums/BlitzMax Programming/Sum of digits

jsp	(Posted 2009) [#1]

I am looking for a very fast function to calculate the sum of digits of a long variable.

Using now a simple loop:

Function QSum2:int(Lo:Long)  
 Local QS:int
 For Local i:Int = 0 To String(Lo).length - 1
  Qs:+Int(String(Lo)[i..i+1])
 Next 
 Return Qs
End Function

But it is definately too slow. Any other ideas are welcome :)

tonyg

(Posted 2009) [#2]

It should be much quicker if you convert your long into a string in one hit rather than keep casting it....

Function tg_qsum2:Int(lo:Long)
  Local QS:Int
  Local instring:String=String(lo)
  Local stringlen:Int=instring.length-1
  For Local i:Int = 0 To stringlen
     Qs:+Int(instring[i..i+1])
  Next 
  Return Qs
End Function

jsp	(Posted 2009) [#3]

Yep, you are right, have absolutely overlooked that.
Thanks!

PGF	(Posted 2009) [#4]

This is about 10 times faster than the original:

Function QSum3:Int(num:Long)
	Local sum:Int = 0
	While num > 0
		sum :+ num Mod 10
		num = num / 10
	Wend
	
	Return sum
End Function

Could be sped up a bit but if you want the ultimate you would be better of with a bit of ASM.

jsp	(Posted 2009) [#5]

Found this just as C function, but wasn't sure if it's faster by using a divide operation in the loop. But it is faster!