• Home
 · 
• Math/Dates
 · 
• multiplication of extra large integers

multiplication of extra large integers

Calculation of the exact value 1000 factorial is nearly impossible by using traditional variables. This code multiplies extra large integers by using strings. 1000! is calculated in 10 seconds

Inputs
two integers in string form

Returns
multiplication result as a string

Rate multiplication of extra large integers

• 1
• 2
• 3
• 4
• 5

(2(2 Vote))

' sample of usage calculation of 1000!
' msgbox may truncate the entire string
' so it is set into clipboard
'Dim Ret As String
'Dim k As Integer
'
'Ret = "1"
'For k = 1 To 1000
' Ret = Multiply(CStr(k), Ret)
'Next
'Clipboard.Clear
'Clipboard.SetText (Ret)
'
'MsgBox Ret
Private Function Multiply(a_num1 As String, a_num2 As String) As String
Dim ls_line() As String
Dim ls1 As String
Dim ls2 As String
Dim ls_mul As String
Dim li_num As Integer
Dim li_mul As Integer
Dim li_elde As Integer
Dim li_sum As Integer
Dim li_maxlen As Integer
Dim li_linecount As Integer
Dim li_up As Integer
Dim k As Long
Dim j As Long
' select larger one
Select Case True
 Case Len(a_num1) >= Len(a_num2)
  ls1 = a_num1
  ls2 = a_num2
 Case Len(a_num1) < Len(a_num2)
  ls1 = a_num2
  ls2 = a_num1
End Select
' start multiplication
li_maxlen = -1
For j = Len(ls2) To 1 Step -1
 li_elde = 0
 ls_mul = ""
 li_num = CInt(Mid(ls2, j, 1)) ' number from right
 For k = Len(ls1) To 1 Step -1
  li_mul = li_num * CInt(Mid(ls1, k, 1)) + li_elde ' ex : 7 times 7 = 49
  If k = 1 Then
   ls_mul = CStr(li_mul) + ls_mul
  Else
   ls_mul = CStr(li_mul Mod 10) + ls_mul ' get 9 from 49
   li_elde = (li_mul - (li_mul Mod 10)) / 10 ' remains 4 from 49
  End If
 Next
 ' add extra zeros to the Right
 For k = 1 To Len(ls2) - j + 1 - 1
  ls_mul = ls_mul + "0"
 Next
 ' store result as a one line string
 ReDim Preserve ls_line(1 To Len(ls2) - j + 1)
 ls_line(Len(ls2) - j + 1) = ls_mul
 If Len(ls_mul) > li_maxlen Then li_maxlen = Len(ls_mul)
Next
li_linecount = UBound(ls_line)
' add extra zeros to the Left
For k = 1 To li_linecount
 li_up = li_maxlen - Len(ls_line(k))
 For j = 1 To li_up
  ls_line(k) = "0" + ls_line(k)
 Next
Next
' start summation
li_elde = 0
ls_mul = ""
For k = li_maxlen To 1 Step -1
 li_sum = 0
 For j = 1 To li_linecount
  li_sum = li_sum + CInt(Mid(ls_line(j), k, 1))
 Next
 li_sum = li_sum + li_elde
 If k = 1 Then
  ls_mul = CStr(li_sum) + ls_mul
 Else
  ls_mul = CStr(li_sum Mod 10) + ls_mul
  li_elde = (li_sum - (li_sum Mod 10)) / 10
 End If
Next
Multiply = ls_mul
End Function