/euler003/Euler003.adb

pragma License ( GPL );
------------------------------------------------------------------------------
-- Author: darkestkhan                                                      --
-- Email:  darkestkhan@gmail.com                                            --
-- License: GNU GPLv3 or any later as published by Free Software Foundation --
-- ( see license.txt file )                                                 --
-- Copyright Š 2011 darkestkhan                                             --
------------------------------------------------------------------------------
-- This Program is Free Software: You Can Redistribute It and/or Modify     --
-- It Under The Terms of The GNU General Public License As Published By     --
-- The Free Software Foundation, Either Version 3 of The License, or        --
-- (at Your Option) Any Later Version.                                      --
--                                                                          --
-- This Program is Distributed in The Hope That It Will Be Useful,          --
-- But WITHOUT ANY WARRANTY; Without Even The Implied Warranty of           --
-- MERCHANTABILITY or FITNESS for A PARTICULAR PURPOSE.  See The            --
-- GNU General Public License for More Details.                             --
--                                                                          --
-- You Should Have Received A Copy of The GNU General Public License        --
-- Along with This Program.  if not, See <Http://Www.Gnu.Org/Licenses/>.    --
------------------------------------------------------------------------------
with TTY;
with Ada.Numerics.Long_Elementary_Functions;
with Ada.Command_Line;
with Ada.Task_Identification;
with Ada.IO_Exceptions;
procedure Euler003 is

  Argc: constant Integer := Ada.Command_Line.Argument_Count;
  Terminal: TTY.TTY;

  task type Largest_Factor ( To_Factorize: Long_Integer );
  task body Largest_Factor is
    Largest_Found: Long_Integer := 1;
    Search_Bound: constant Long_Integer := Long_Integer ( Ada.Numerics.Long_Elementary_Functions.Sqrt ( Long_Float ( To_Factorize ) ) ) + 1;
    -- conversion from float to long_integer may cause rounding error, in which case number that would be properly factored won't be ( consider 169 )
    Divisor: Long_Integer := 3;
    Number: Long_Integer := To_Factorize;
  begin
    if Number mod 2 = 0 then
      Largest_Found := 2;
    end if;
    while Number mod 2 = 0 loop
      Number := Number / 2;
    end loop;
    -- check for divisibility by 2
    while Divisor < Search_Bound and then Number /= 1 loop
      if Number mod Divisor = 0 then
        if Divisor > Largest_Found then
          Largest_Found := Divisor;
        end if;
        -- factor may be bigger than the one previously found
        while Number mod Divisor = 0 loop
          Number := Number / Divisor;
        end loop;
        -- number may be factored even many times by given factor, not factoring may result in false result ( consider 27 )
      end if;
      -- number was checked given ( possible ) factor so move on next
      Divisor := Divisor + 2;
    end loop;
    -- factorize ( trial division )
    if Number > Largest_Found then
      Largest_Found := Number;
    end if;
    -- it may be possible that to_factorize is prime number in which case it itself is the largest factor ( consider 13 )
    -- it may be also possible that it was coprime ( consider 26 )
    Terminal.Write_Line ( "Largest factor of " & To_Factorize'img & " is " & Largest_Found'img ); 
    Ada.Task_Identification.Abort_Task ( Ada.Task_Identification.Current_Task );
  end Largest_Factor;

  function Create ( To_Factorize: in Long_Integer ) return access Largest_Factor is
  begin
    return new Largest_Factor ( To_Factorize => To_Factorize );
  end Create;

  type Factorizing_Array is array ( Integer range <> ) of access Largest_Factor;
  Factorizers: Factorizing_Array ( 1 .. Argc );

  task type Creator;
  task body Creator is
    To_Factorize: Long_Integer;
  begin
    if Argc = 0 then
      Terminal.Write_Line ( "Usage: " & Ada.Command_Line.Command_Name & " [int] ... " );
      Ada.Task_Identification.Abort_Task ( Ada.Task_Identification.Current_Task );
    else
      for Index in 1 .. Argc loop
        To_Factorize := Long_Integer'Value ( Ada.Command_Line.Argument ( Index ) );
        Factorizers ( Index ) := Create ( To_Factorize => To_Factorize );
      end loop;
    end if;
  exception
    when Ada.IO_Exceptions.Data_Error => Terminal.Write_Line ( "One of arguments was too big. Aborting. Aborting." );
  end Creator;

  God: Creator;
  -- devil: destructor;

begin
  null;
end Euler003;