Karatsuba solution in Scala. Works with negative numbers also.

Karatsuba.scala

// Karatsuba solution in Scala. Works with negative numbers also.
// https://en.wikipedia.org/wiki/Karatsuba_algorithm

object Karatsuba {
  import scala.math._

def split(x:Int, y:Int)={
 val absx=abs(x)
 val absy=abs(y)
 val m=max(absx.toString.length(),absy.toString.length())
 val xpadded=s"%0${m}d".format(absx)
 val ypadded=s"%0${m}d".format(absy)
 val xpbits=xpadded.splitAt(m/2)
 val ypbits=ypadded.splitAt(m/2)
 val polx=signum(x)
 val poly=signum(y)
 
 ((xpbits._1.toInt*polx,xpbits._2.toInt*polx),
  (ypbits._1.toInt*poly,ypbits._2.toInt*poly),m-m/2)
}                                                 

def multiply(x: Int, y: Int): Int = {
  if (abs(x)<10||abs(y)<10) x * y
  else {
    val ((a,b),(c,d),rest) = split(x,y)

    val ac= multiply(a,c)
    val bd= multiply(b,d)
    
    val ad_plus_bc= multiply(a + b, c + d) - ac - bd
    
    val _10rest = pow(10, rest).toInt
    val _10rest2 = _10rest*_10rest
    
    _10rest2*ac + _10rest*ad_plus_bc + bd
  }
}                                                 

assert(multiply(5678, 1234)==7006652)
assert(multiply(131,46)==6026)

assert(multiply(123400,-10)== -1234000)
}