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--  Programmed by Jedidiah Barber
--  Licensed under the Sunset License v1.0

--  See license.txt for further details


package body Kompsos.Arithmetic is


    ---------------
    --  Numbers  --
    ---------------

    function Is_Number
           (Item : in Term)
        return Boolean is
    begin
        if Item.Kind = Null_Term then
            return True;
        elsif Item.Kind = Pair_Term and then Item.Left.Kind = Atom_Term then
            if Item.Right.Kind = Null_Term then
                return Item.Left.Atom = One_Element;
            else
                return (Item.Left.Atom = Zero_Element or else Item.Left.Atom = One_Element) and then
                    Is_Number (Item.Right);
            end if;
        else
            return False;
        end if;
    end Is_Number;


    function Build
           (Value : in Natural)
        return Term is
    begin
        if Value = 0 then
            return Empty_Term;
        elsif Value mod 2 = 0 then
            return T (T (Zero_Element), Build (Value / 2));
        else
            return T (T (One_Element), Build ((Value - 1) / 2));
        end if;
    end Build;


    function Value
           (Item : in Term)
        return Natural is
    begin
        if Item.Kind = Null_Term then
            return 0;
        elsif Item.Left.Atom = Zero_Element then
            return 2 * Value (Item.Right);
        else
            return 1 + 2 * Value (Item.Right);
        end if;
    end Value;




    ------------------
    --  Operations  --
    ------------------

    --  full-addero  --

    function Full_Adder
           (This   : in Goal;
            Inputs : in Term_Array)
        return Goal
    is
        Cin_Term  : Term renames Inputs (1);
        A_Term    : Term renames Inputs (2);
        B_Term    : Term renames Inputs (3);
        Sum_Term  : Term renames Inputs (4);
        Cout_Term : Term renames Inputs (5);

        Outputs : Goal_Array := (1 .. 8 => This);
    begin
        Outputs (1).Unify (Cin_Term,  Zero_Element);    Outputs (2).Unify (Cin_Term,   One_Element);
        Outputs (1).Unify (A_Term,    Zero_Element);    Outputs (2).Unify (A_Term,    Zero_Element);
        Outputs (1).Unify (B_Term,    Zero_Element);    Outputs (2).Unify (B_Term,    Zero_Element);
        Outputs (1).Unify (Sum_Term,  Zero_Element);    Outputs (2).Unify (Sum_Term,   One_Element);
        Outputs (1).Unify (Cout_Term, Zero_Element);    Outputs (2).Unify (Cout_Term, Zero_Element);

        Outputs (3).Unify (Cin_Term,  Zero_Element);    Outputs (4).Unify (Cin_Term,   One_Element);
        Outputs (3).Unify (A_Term,     One_Element);    Outputs (4).Unify (A_Term,     One_Element);
        Outputs (3).Unify (B_Term,    Zero_Element);    Outputs (4).Unify (B_Term,    Zero_Element);
        Outputs (3).Unify (Sum_Term,   One_Element);    Outputs (4).Unify (Sum_Term,  Zero_Element);
        Outputs (3).Unify (Cout_Term, Zero_Element);    Outputs (4).Unify (Cout_Term,  One_Element);

        Outputs (5).Unify (Cin_Term,  Zero_Element);    Outputs (6).Unify (Cin_Term,   One_Element);
        Outputs (5).Unify (A_Term,    Zero_Element);    Outputs (6).Unify (A_Term,    Zero_Element);
        Outputs (5).Unify (B_Term,     One_Element);    Outputs (6).Unify (B_Term,     One_Element);
        Outputs (5).Unify (Sum_Term,   One_Element);    Outputs (6).Unify (Sum_Term,  Zero_Element);
        Outputs (5).Unify (Cout_Term, Zero_Element);    Outputs (6).Unify (Cout_Term,  One_Element);

        Outputs (7).Unify (Cin_Term,  Zero_Element);    Outputs (8).Unify (Cin_Term,   One_Element);
        Outputs (7).Unify (A_Term,     One_Element);    Outputs (8).Unify (A_Term,     One_Element);
        Outputs (7).Unify (B_Term,     One_Element);    Outputs (8).Unify (B_Term,     One_Element);
        Outputs (7).Unify (Sum_Term,  Zero_Element);    Outputs (8).Unify (Sum_Term,   One_Element);
        Outputs (7).Unify (Cout_Term,  One_Element);    Outputs (8).Unify (Cout_Term,  One_Element);

        return Disjunct (Outputs);
    end Full_Adder;


    procedure Full_Adder
           (This   : in out Goal;
            Inputs : in     Term_Array) is
    begin
        This := Full_Adder (This, Inputs);
    end Full_Adder;



    --  poso  --

    function GT_Zero
           (This     : in Goal;
            Num_Term : in Term'Class)
        return Goal is
    begin
        return This.Pair (Num_Term);
    end GT_Zero;


    procedure GT_Zero
           (This     : in out Goal;
            Num_Term : in     Term'Class) is
    begin
        This := GT_Zero (This, Num_Term);
    end GT_Zero;



    --  >1o  --

    function GT_One
           (This     : in Goal;
            Num_Term : in Term'Class)
        return Goal
    is
        Result : Goal := This;
        Ref_Term : constant Term := Result.Fresh;
    begin
        Result.Tail (Num_Term & Ref_Term);
        Result.Pair (Ref_Term);
        return Result;
    end GT_One;


    procedure GT_One
           (This     : in out Goal;
            Num_Term : in     Term'Class) is
    begin
        This := GT_One (This, Num_Term);
    end GT_One;



    --  addero  --

    function Adder
           (This   : in Goal;
            Inputs : in Term_Array)
        return Goal
    is
        Cin_Term    : Term renames Inputs (1);
        N_Term      : Term renames Inputs (2);
        M_Term      : Term renames Inputs (3);
        Result_Term : Term renames Inputs (4);

        Outputs : Goal_Array := (1 .. 8 => This);
    begin
        Outputs (1).Unify (Cin_Term, Zero_Element);
        Outputs (1).Unify (M_Term, Zero_Term);
        Outputs (1).Unify (N_Term, Result_Term);

        Outputs (2).Unify (Cin_Term, Zero_Element);
        Outputs (2).Unify (N_Term, Zero_Term);
        Outputs (2).Unify (M_Term, Result_Term);
        GT_Zero (Outputs (2), M_Term);

        Outputs (3).Unify (Cin_Term, One_Element);
        Outputs (3).Unify (M_Term, Zero_Term);
        Outputs (3).Conjunct (Adder_Access, T (Zero_Element) & N_Term & One_Term & Result_Term);

        Outputs (4).Unify (Cin_Term, One_Element);
        Outputs (4).Unify (N_Term, Zero_Term);
        GT_Zero (Outputs (4), M_Term);
        Outputs (4).Conjunct (Adder_Access, T (Zero_Element) & One_Term & M_Term & Result_Term);

        Outputs (5).Unify (N_Term, One_Term);
        Outputs (5).Unify (M_Term, One_Term);
        declare
            A_Var : constant Term := Outputs (5).Fresh;
            C_Var : constant Term := Outputs (5).Fresh;
        begin
            Outputs (5).Unify (T (A_Var, C_Var), Result_Term);
            Full_Adder (Outputs (5), Cin_Term & T (One_Element) & T (One_Element) & A_Var & C_Var);
        end;

        Outputs (6).Unify (N_Term, One_Term);
        GT_One (Outputs (6), M_Term);
        Outputs (6).Conjunct (General_Adder_Access, Inputs);

        Outputs (7).Unify (M_Term, One_Term);
        GT_One (Outputs (7), N_Term);
        GT_One (Outputs (7), Result_Term);
        Outputs (7).Conjunct (Adder_Access, Cin_Term & One_Term & N_Term & Result_Term);

        GT_One (Outputs (8), N_Term);
        GT_One (Outputs (8), M_Term);
        Outputs (8).Conjunct (General_Adder_Access, Inputs);

        return Disjunct (Outputs);
    end Adder;


    procedure Adder
           (This   : in out Goal;
            Inputs : in     Term_Array) is
    begin
        This := Adder (This, Inputs);
    end Adder;



    --  gen-addero  --

    function General_Adder
           (This   : in Goal;
            Inputs : in Term_Array)
        return Goal
    is
        Cin_Term    : Term renames Inputs (1);
        N_Term      : Term renames Inputs (2);
        M_Term      : Term renames Inputs (3);
        Result_Term : Term renames Inputs (4);

        Result : Goal := This;

        A_Var : constant Term := Result.Fresh;
        B_Var : constant Term := Result.Fresh;
        C_Var : constant Term := Result.Fresh;
        D_Var : constant Term := Result.Fresh;
        X_Var : constant Term := Result.Fresh;
        Y_Var : constant Term := Result.Fresh;
        Z_Var : constant Term := Result.Fresh;
    begin
        Result.Unify (T (A_Var, X_Var), N_Term);
        Result.Unify (T (B_Var, Y_Var), M_Term);
        GT_Zero (Result, Y_Var);
        Result.Unify (T (C_Var, Z_Var), Result_Term);
        GT_Zero (Result, Z_Var);
        Full_Adder (Result, Cin_Term & A_Var & B_Var & C_Var & D_Var);
        Result.Conjunct (Adder_Access, D_Var & X_Var & Y_Var & Z_Var);
        return Result;
    end General_Adder;


    procedure General_Adder
           (This   : in out Goal;
            Inputs : in     Term_Array) is
    begin
        This := General_Adder (This, Inputs);
    end General_Adder;



    --  +o  --

    function Add
           (This   : in Goal;
            Inputs : in Term_Array)
        return Goal is
    begin
        return Adder (This, T (Zero_Element) & Inputs);
    end Add;


    procedure Add
           (This   : in out Goal;
            Inputs : in     Term_Array) is
    begin
        This := Add (This, Inputs);
    end Add;



    --  -o  --

    function Subtract
           (This   : in Goal;
            Inputs : in Term_Array)
        return Goal
    is
        N_Term      : Term renames Inputs (1);
        M_Term      : Term renames Inputs (2);
        Result_Term : Term renames Inputs (3);
    begin
        return Add (This, M_Term & Result_Term & N_Term);
    end Subtract;


    procedure Subtract
           (This   : in out Goal;
            Inputs : in     Term_Array) is
    begin
        This := Subtract (This, Inputs);
    end Subtract;


end Kompsos.Arithmetic;