Compare Strings 'naturally', i.e. respecting embedded integers

NaturalCompare.scala

def naturalCompare( a: String, b: String ) : Int = {
   val asz = a.length()
   val bsz = b.length()
   var sz  = math.min( asz, bsz )
   var ai  = 0
   var bi  = 0
   while( ai < asz && bi < bsz ) {
      val ac = a.charAt( ai ).toUpperCase
      val bc = b.charAt( bi ).toUpperCase
      if( ac.isDigit && bc.isDigit ) {
         val aj = ai
         while( ai < asz && a.charAt( ai ).isDigit ) { ai += 1 }
         val an = a.substring( aj, ai ).toInt
         val bj = bi
         while( bi < bsz && b.charAt( bi ).isDigit ) { bi += 1 }
         val bn = b.substring( bj, bi ).toInt
         if( an < bn ) return -1 else if( an > bn ) return 1
      } else {
         if( ac < bc ) return -1 else if( ac > bc ) return 1
         ai += 1; bi += 1
      }
   }
   val ar = asz - ai
   val br = bsz - bi
   if( ar < br ) return -1 else if( ar > br ) return 1
   0 // equal
}

val test = Seq( "Ch-1 1", "Ch-1 2", "Ch-1 10", "Ach-33", "666-Gaga", "Ch-12 1" )
test.sortWith( naturalCompare( _, _ ) < 0 )