Microsoft Small Basic

Program Listing: HHW468-2

List Program

' Factorial of Big Number
' Copyright (c) 2012, 2013 Nonki Takahashi. All right reserved.
'
' History:
' 0.2 2013/03/03 Enabled to input n. (HHW468-2)
' 0.1 2012/04/28 Bug fixed version. (HHW468-1)
'
DIGITS = 13 ' separate big number to avoid overflow within this digits
POW10DIG = Math.Power(10, DIGITS)
Z="0000000000000000000000000"
COMMA = ""
TextWindow.WriteLine("Factorial Calculator v0.2")
While "True"
TextWindow.Write("n? ")
n = TextWindow.ReadNumber()
t0 = Clock.ElapsedMilliseconds
ans = 1
For i = 1 to n
a = ans
b = i
Mul() ' ans = a * b
EndFor
TextWindow.Write(n + "!=")
x = ans
PrintWithComma()
t1 = Clock.ElapsedMilliseconds
TextWindow.WriteLine("(" + (t1 - t0) + "ms)")
EndWhile
' end of program

Sub Mul
' Mul - Multiply a by b
' const DIGITS = 13
' const POW10DIG = 10^DIGITS
' const Z = "0000000000000000000000000"
' param a
' param b
' return ans = a * b
Stack.PushValue("param", i)
Stack.PushValue("param", n)

s = Text.GetLength(a)
While s >= 1 And Text.GetSubText(a, s, 1) = "0"
s = s - 1
EndWhile
If s = 0 Then
ans = 0
Goto mul_return
EndIf
az = Text.GetSubTextToEnd(a, s + 1)
an = Text.GetSubText(a, 1, s)
la = Text.GetLength(an)
m = Math.Ceiling(la / DIGITS)

s = Text.GetLength(b)
While s >= 1 And Text.GetSubText(b, s, 1) = "0"
s = s - 1
EndWhile
If s = 0 Then
ans = 0
Goto mul_return
EndIf
bz = Text.GetSubTextToEnd(b, s + 1)
bn = Text.GetSubText(b, 1, s)
lb = Text.GetLength(bn)
n = Math.Ceiling(lb / DIGITS)

For k = 1 To n + m
ab[k] = 0
EndFor
For i = 1 To n
For j = 1 To m
If j < m Then
s = la - DIGITS * j + 1
l = DIGITS
Else ' j = m
s = 1
l = Math.Remainder(la - 1, DIGITS) + 1
EndIf
aj = Text.GetSubText(an, s, l)
If i < n Then
s = lb - DIGITS * i + 1
l = DIGITS
Else ' i = n
s = 1
l = Math.Remainder(lb - 1, DIGITS) + 1
EndIf
bi = Text.GetSubText(bn, s, l)
x = aj * bi
k = i + j
l = Text.GetLength(x)
s = l - DIGITS + 1
If s < 1 Then
s = 1
xn = Text.GetSubText(x, s, l)
xc = 0
Else
l = DIGITS
xn = Text.GetSubText(x, s, l)
xc = Text.GetSubText(x, 1, s - 1)
EndIf
ab[k] = ab[k] + xc
ab[k - 1] = ab[k - 1] + xn
While (k - 1 <= n + m) And (ab[k - 1] >= POW10DIG)
l = Text.GetLength(ab[k - 1])
s = l - DIGITS + 1
If s < 1 Then
s = 1
xn = Text.GetSubText(ab[k - 1], s, l)
xc = 0
Else
l = DIGITS
xn = Text.GetSubText(ab[k - 1], s, l)
xc = Text.GetSubText(ab[k - 1], 1, s - 1)
EndIf
ab[k] = ab[k] + xc
ab[k - 1] = xn
k = k + 1
EndWhile
EndFor
EndFor
ans = ""
For k = 1 To n + m - 2
ans = Text.Append(ab[k], ans)
l = DIGITS * k - Text.GetLength(ans)
If l > 0 Then
ans = Text.Append(Text.GetSubText(Z, 1, l), ans)
EndIf
EndFor
' k = n + m - 1
ans = Text.Append(ab[k], ans)
l = DIGITS * k - Text.GetLength(ans)
If (l > 0) And (ab[k + 1] > 0) Then
ans = Text.Append(Text.GetSubText(Z, 1, l), ans)
EndIf
k = k + 1
' k = n + m
If ab[k] > 0 Then
ans = Text.Append(ab[k], ans)
EndIf
ans = Text.Append(ans, az)
ans = Text.Append(ans, bz)
mul_return:
n = Stack.PopValue("param")
i = Stack.PopValue("param")
EndSub

Sub PrintWithComma
' const COMMA = "," or "." or " " or "" etc.
' param x
l = Text.GetLength(x)
n = Math.Ceiling(l / 3)
l = Math.Remainder(l, 3)
If l = 0 Then
l = 3
EndIf
s = 1
For i = 1 To n
TextWindow.Write(Text.GetSubText(x, s, l))
If i < n Then
TextWindow.Write(COMMA)
EndIf
s = s + l
l = 3
EndFor
TextWindow.WriteLine("")
EndSub