-- This file is  free  software, which  comes  along  with  SmallEiffel. This
-- software  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. You can modify it as you want, provided
-- this header is kept unaltered, and a notification of the changes is added.
-- You  are  allowed  to  redistribute  it and sell it, alone or as a part of 
-- another product.
--          Copyright (C) 1994-98 LORIA - UHP - CRIN - INRIA - FRANCE
--            Dominique COLNET and Suzanne COLLIN - colnet@loria.fr 
--                       http://SmallEiffel.loria.fr
--
deferred class ABSTRACT_FRACTION 
--
-- To implement NUMBER (do not use this class, see NUMBER).
--
       
inherit NUMBER;

feature 
   
   is_zero: BOOLEAN is false;
   
   is_one: BOOLEAN is false;
   
   frozen to_integer: INTEGER is
      do
	 check false end;
      end;
   
   infix "@=" (other: INTEGER): BOOLEAN is do end;
   
   infix "//"(other: NUMBER): NUMBER is
      do
	 check false end;
      end;
   
   infix "@//"(other: INTEGER): NUMBER is
      do
	 check false end;
      end;
   
   infix "\\"(other: NUMBER): NUMBER is
      do
	 check false end;
      end;
   
   infix "@\\"(other: INTEGER): NUMBER is
      do
	 check false end;
      end;
   
feature {NUMBER}
   
   from_two_integer(n, d: INTEGER): NUMBER is
      local
	 num, den, g: INTEGER;
      do
	 g := n.abs.gcd(d.abs);
	 num := n.abs // g;
	 den := d.abs // g;
	 if (den = 1) then
	    if (n < 0) xor (d < 0) then
	       !SMALL_INTEGER!Result.make(-num);
	    else
	       !SMALL_INTEGER!Result.make(num);
	    end;
	 else
	    if (n < 0) xor (d < 0) then
	       !SMALL_FRACTION!Result.make(-num,den);
	    else
	       !SMALL_FRACTION!Result.make(num,den);
	    end;
	 end;
      end;
   
   from_two_abstract_integer(n, d: ABSTRACT_INTEGER): NUMBER is
      local
	 num, den : ABSTRACT_INTEGER;
	 n_abs, g: ABSTRACT_INTEGER;
      do
	 n_abs ?= n.abs; 
	 g := n_abs.gcd(d.abs);
	 if (g @= 1) then
	    num := n;
	    den := d;
	 else
	    num ?= n // g;     
	    den ?= d // g;
	 end;
	 if (den.is_one) then
	    Result := num;
	 else	    
	    num ?= num.abs;
	    den ?= den.abs;
	    if num.is_integer and then den.is_integer and then (n.is_negative xor d.is_negative) then
	       !SMALL_FRACTION!Result.make(-num.to_integer,den.to_integer);
	    elseif (num.is_integer and then den.is_integer) then 
	       !SMALL_FRACTION!Result.make(num.to_integer,den.to_integer);
	    else
	       !LARGE_FRACTION!Result.make_simply(num,den,(n.is_negative xor d.is_negative));
	    end;	 
	 end;
      end;
   
   from_integer_and_abstract_integer(n: INTEGER; d: ABSTRACT_INTEGER): NUMBER is
      require
	 d /= Void;
      local
	 num: ABSTRACT_INTEGER;
      do
	 if (n = Minimum_integer) then
	    num := greater_large_negative_integer;
	 else
	    !SMALL_INTEGER!num.make(n);
	 end;
	 Result := from_two_abstract_integer(num,d);
      end;   
   
   from_abstract_integer_and_integer(n: ABSTRACT_INTEGER; d: INTEGER): NUMBER is
      require
	 n /= Void;
      local
	 den: ABSTRACT_INTEGER;
      do
	 if (d = Minimum_integer) then
	    den := greater_large_negative_integer;
	 else
	    !SMALL_INTEGER!den.make(d);
	 end;
	 Result := from_two_abstract_integer(n,den); 
      end;   
   
   
end -- class ABSTRACT_FRACTION