Task: Long multiplication



C#: using System;
using static System.Console;
using BI = System.Numerics.BigInteger;

class Program {

  static decimal mx = 1E28M, hm = 1E14M, a;

  
  struct bi { public decimal hi, lo; }

  
  static bi set4sq(decimal a) { bi r; r.hi = Math.Floor(a / hm); r.lo = a % hm; return r; }

  
  static string toStr(bi a, bool comma = false) {
    string r = a.hi == 0 ? string.Format("{0:0}", a.lo) :
                           string.Format("{0:0}{1:" + new string('0', 28) + "}", a.hi, a.lo);
    if (!comma) return r;  string rc = "";
    for (int i = r.Length - 3; i > 0; i -= 3) rc = "," + r.Substring(i, 3) + rc;
    return r.Substring(0, ((r.Length + 2) % 3) + 1) + rc; }

  
  static decimal Pow_dec(decimal bas, uint exp) {
    if (exp == 0) return 1M; decimal tmp = Pow_dec(bas, exp >> 1); tmp *= tmp;
    if ((exp & 1) == 0) return tmp; return tmp * bas; }

  static void Main(string[] args) {
    for (uint p = 64; p < 95; p += 30) {        
      bi x = set4sq(a = Pow_dec(2M, p)), y;     
      WriteLine("The square of (2^{0}):                    {1,38:n0}", p, a); BI BS = BI.Pow((BI)a, 2);
      y.lo = x.lo * x.lo; y.hi = x.hi * x.hi;   
      a = x.hi * x.lo * 2M;                     
      y.hi += Math.Floor(a / hm);               
      y.lo += (a % hm) * hm;                    
      while (y.lo > mx) { y.lo -= mx; y.hi++; } 
      WriteLine(" is {0,75} (which {1} match the BigInteger computation)\n", toStr(y, true),
          BS.ToString() == toStr(y) ? "does" : "fails to"); } }

}






VB: Imports System
Imports System.Console
Imports BI = System.Numerics.BigInteger

Module Module1

    Dim a As Decimal, mx As Decimal = 1E28D, hm As Decimal = 1E14D

    
    Structure bd
        Public hi, lo As Decimal
    End Structure

    
    Function toStr(ByVal a As bd, ByVal Optional comma As Boolean = False) As String
        Dim r As String = If(a.hi = 0, String.Format("{0:0}", a.lo),
                                       String.Format("{0:0}{1:" & New String("0"c, 28) & "}", a.hi, a.lo))
        If Not comma Then Return r 
        Dim rc As String = ""
        For i As Integer = r.Length - 3 To 0 Step -3
            rc = "," & r.Substring(i, 3) & rc : Next
        toStr = r.Substring(0, r.Length Mod 3) & rc
            toStr = toStr.Substring(If(toStr.Chars(0) = "," , 1, 0))
    End Function

    
    Function Pow_dec(ByVal bas As Decimal, ByVal exp As UInteger) As Decimal
        If exp = 0 Then Pow_dec = 1D else Pow_dec = Pow_dec(bas, exp >> 1) : _
        Pow_dec *= Pow_dec : If (exp And 1) <> 0 Then Pow_dec *= bas
    End Function

    Sub Main(ByVal args As String())
         For p As UInteger = 64 To 95 - 1 Step 30                 
            Dim y As bd, x As bd : a = Pow_dec(2D, p)             
            WriteLine("The square of (2^{0}):                    {1,38:n0}", p, a)
            x.hi = Math.Floor(a / hm) : x.lo = a Mod hm           
            Dim BS As BI = BI.Pow(CType(a, BI), 2)                
            y.lo = x.lo * x.lo : y.hi = x.hi * x.hi               
            a = x.hi * x.lo * 2D                                  
            y.hi += Math.Floor(a / hm) : y.lo += (a Mod hm) * hm  
            While y.lo > mx : y.lo -= mx : y.hi += 1 : End While  
            WriteLine(" is {0,75} (which {1} match the BigInteger computation)" & vbLf,
                toStr(y, True), If(BS.ToString() = toStr(y), "does", "fails to"))
        Next
    End Sub

End Module