/// <summary> /// Calculates a product of a two ALong instances, a.k.a "School" method (very slow) /// </summary> /// <param name="num1">Multiplicand</param> /// <param name="num2">Multiplier</param> /// <returns>Product of num1 and num2.</returns> //TODO: replace with Karatsuba, Schönhage–Strassen or Knuth. (Fast Fourier transform?). //TODO: use base of size of Int32 to "shorten" sizes of numbers within multiplication speed being kept. public static ALong Mul(ALong num1, ALong num2) { var result = new ALong(0); if (num1 == 0 || num2 == 0) { return(result); } var carry = 0; for (int i = 0; i < num1.Length(); i++) { var n1 = num1.GetRNumAtIndex(i); var res = String.Empty; var n2len = num2.Length(); carry = 0; for (int k = 0; k < n2len; k++) { var n2 = num2.GetRNumAtIndex(k); var ns = n1 * n2 + carry; carry = ns / 10; res = (ns % 10) + res; if (k == n2len - 1 && carry > 0) { res = carry.ToString() + res; } } var mulres = new ALong(res); mulres.MulBase(i); result += mulres; } if (num1.IsNegative != num2.IsNegative) { result.SetNegative(true); } return(result); }
/// <summary> /// Calculates a Summary of a two ALong absolute values, a.k.a "School" method. /// </summary> /// <param name="num1">First addend</param> /// <param name="num2">Second addend</param> /// <returns>ALong instance representing a sum of two addends.</returns> private static ALong AbsSum(ALong num1, ALong num2) { var result = String.Empty; int carry = 0; var max = Math.Max(num1.Length(), num2.Length()); for (int i = 0; i < max; i++) { var n1 = num1.GetRNumAtIndex(i); var n2 = num2.GetRNumAtIndex(i); var ns = n1 + n2 + carry; carry = 0; if (ns >= 10) { ns = ns - 10; carry = 1; } result = ns.ToString() + result; if (i == max - 1 && carry > 0) { result = carry.ToString() + result; } } return(new ALong(result)); }