/// <summary>
/// multiplies 2 digits given their positions
/// </summary>
/// <param name="digit1"></param>
/// <param name="digit2"></param>
/// <param name="digit1Pos"></param>
/// <param name="digit2Pos"></param>
/// <returns></returns>
private Numeric MultiplyDigits(string digit1, string digit2,
Numeric digit1Pos, Numeric digit2Pos)
{
Debug.WriteLine("multiplying digits {0} and {1} at positions {2} and {3}",
digit1, digit2, digit1Pos.SymbolsText, digit2Pos.SymbolsText);
var val = this._multMap.Get(digit1, digit2);
Debug.WriteLine("{0} * {1} = {2}",
digit1, digit2, val.SymbolsText);
var rv = val.Clone().HasShift();
var number1 = Numeric.New(this.NumberSystem, digit1).HasShift();
var number2 = Numeric.New(this.NumberSystem, digit2).HasShift();
var counter = digit1Pos.HasAddition();
rv.ShiftRight(counter);
number1.ShiftRight(counter);
counter = digit2Pos.HasAddition();
rv.ShiftRight(counter);
number2.ShiftRight(counter);
Debug.WriteLine("equivalent to {0} * {1} = {2}",
number1.SymbolsText, number2.SymbolsText, rv.SymbolsText);
return rv.InnermostNumeric;
}