' FB 1.05.0 Win64

#include "gmp.bi"

Sub leftFactorial(rop As __mpz_struct, op As ULong)
  Dim As __mpz_struct t1
  mpz_init_set_ui(@t1, 1)
  mpz_set_ui(@rop, 0)
  For i As ULong = 1 To op
    mpz_add(@rop, @rop, @t1)
    mpz_mul_ui(@t1, @t1, i)
  Next
  mpz_clear(@t1)
End Sub

Function digitCount(op As __mpz_struct) As ULong
  Dim As ZString Ptr t = mpz_get_str(0, 10, @op)
  Dim As ULong ret = Len(*t)
  Deallocate(t)
  Return ret
End Function

Dim As __mpz_struct t
mpz_init(@t)

For i As ULong = 0 To 110
  If i <= 10 OrElse i Mod 10 = 0 Then
    leftFactorial(t, i)
    gmp_printf(!"!%u = %Zd\n", i, @t)
  End If
Next

Print

For i As ULong = 1000 To 10000 Step 1000
  leftFactorial(t, i)
  Print "!"; Str(i); " has "; digitCount(t); " digits"
Next

mpz_clear(@t)
Print
Print "Press any key to quit"
Sleep