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------------------------------------------------------------------------------

--                                                                          --

--                         GNAT RUN-TIME COMPONENTS                         --

--                                                                          --

--               G N A T . M B B S _ F L O A T _ R A N D O M                --

--                                                                          --

--                                 B o d y                                  --

--                                                                          --

--          Copyright (C) 1992-2010, Free Software Foundation, Inc.         --

--                                                                          --

-- GNAT is free software;  you can  redistribute it  and/or modify it under --

-- terms of the  GNU General Public License as published  by the Free Soft- --

-- ware  Foundation;  either version 3,  or (at your option) any later ver- --

-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --

-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --

-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --

--                                                                          --

-- As a special exception under Section 7 of GPL version 3, you are granted --

-- additional permissions described in the GCC Runtime Library Exception,   --

-- version 3.1, as published by the Free Software Foundation.               --

--                                                                          --

-- You should have received a copy of the GNU General Public License and    --

-- a copy of the GCC Runtime Library Exception along with this program;     --

-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --

-- <http://www.gnu.org/licenses/>.                                          --

--                                                                          --

-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

------------------------------------------------------------------------------

with Ada.Calendar;

package body GNAT.MBBS_Float_Random is

   -------------------------

   -- Implementation Note --

   -------------------------

   --  The design of this spec is a bit awkward, as a result of Ada 95 not

   --  permitting in-out parameters for function formals (most naturally

   --  Generator values would be passed this way). In pure Ada 95, the only

   --  solution would be to add a self-referential component to the generator

   --  allowing access to the generator object from inside the function. This

   --  would work because the generator is limited, which prevents any copy.

   --  This is a bit heavy, so what we do is to use Unrestricted_Access to

   --  get a pointer to the state in the passed Generator. This works because

   --  Generator is a limited type and will thus always be passed by reference.

   package Calendar renames Ada.Calendar;

   type Pointer is access all State;

   -----------------------

   -- Local Subprograms --

   -----------------------

   procedure Euclid (P, Q : Int; X, Y : out Int; GCD : out Int);

   function  Euclid (P, Q : Int) return Int;

   function Square_Mod_N (X, N : Int) return Int;

   ------------

   -- Euclid --

   ------------

   procedure Euclid (P, Q : Int; X, Y : out Int; GCD : out Int) is

      XT : Int := 1;

      YT : Int := 0;

      procedure Recur

        (P,  Q  : Int;                    --  a (i-1), a (i)

         X,  Y  : Int;                    --  x (i),   y (i)

         XP, YP : in out Int;             --  x (i-1), y (i-1)

         GCD    : out Int);

      procedure Recur

        (P,  Q  : Int;

         X,  Y  : Int;

         XP, YP : in out Int;

         GCD    : out Int)

      is

         Quo : Int := P / Q;              --  q <-- |_ a (i-1) / a (i) _|

         XT  : Int := X;                  --  x (i)

         YT  : Int := Y;                  --  y (i)

      begin

         if P rem Q = 0 then                 --  while does not divide

            GCD := Q;

            XP  := X;

            YP  := Y;

         else

            Recur (Q, P - Q * Quo, XP - Quo * X, YP - Quo * Y, XT, YT, Quo);

            --  a (i) <== a (i)

            --  a (i+1) <-- a (i-1) - q*a (i)

            --  x (i+1) <-- x (i-1) - q*x (i)

            --  y (i+1) <-- y (i-1) - q*y (i)

            --  x (i) <== x (i)

            --  y (i) <== y (i)

            XP  := XT;

            YP  := YT;

            GCD := Quo;

         end if;

      end Recur;

   --  Start of processing for Euclid

   begin

      Recur (P, Q, 0, 1, XT, YT, GCD);

      X := XT;

      Y := YT;

   end Euclid;

   function Euclid (P, Q : Int) return Int is

      X, Y, GCD : Int;

      pragma Unreferenced (Y, GCD);

   begin

      Euclid (P, Q, X, Y, GCD);

      return X;

   end Euclid;

   -----------

   -- Image --

   -----------

   function Image (Of_State : State) return String is

   begin

      return Int'Image (Of_State.X1) & ',' & Int'Image (Of_State.X2)

             & ',' &

             Int'Image (Of_State.P)  & ',' & Int'Image (Of_State.Q);

   end Image;

   ------------

   -- Random --

   ------------

   function Random  (Gen : Generator) return Uniformly_Distributed is

      Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;

   begin

      Genp.X1 := Square_Mod_N (Genp.X1,  Genp.P);

      Genp.X2 := Square_Mod_N (Genp.X2,  Genp.Q);

      return

        Float ((Flt (((Genp.X2 - Genp.X1) * Genp.X)

                  mod Genp.Q) * Flt (Genp.P)

          + Flt (Genp.X1)) * Genp.Scl);

   end Random;

   -----------

   -- Reset --

   -----------

   --  Version that works from given initiator value

   procedure Reset (Gen : Generator; Initiator : Integer) is

      Genp   : constant Pointer := Gen.Gen_State'Unrestricted_Access;

      X1, X2 : Int;

   begin

      X1 := 2 + Int (Initiator) mod (K1 - 3);

      X2 := 2 + Int (Initiator) mod (K2 - 3);

      --  Eliminate effects of small initiators

      for J in 1 .. 5 loop

         X1 := Square_Mod_N (X1, K1);

         X2 := Square_Mod_N (X2, K2);

      end loop;

      Genp.all :=

        (X1  => X1,

         X2  => X2,

         P   => K1,

         Q   => K2,

         X   => 1,

         Scl => Scal);

   end Reset;

   --  Version that works from specific saved state

   procedure Reset (Gen : Generator; From_State : State) is

      Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;

   begin

      Genp.all := From_State;

   end Reset;

   --  Version that works from calendar

   procedure Reset (Gen : Generator) is

      Genp   : constant Pointer       := Gen.Gen_State'Unrestricted_Access;

      Now    : constant Calendar.Time := Calendar.Clock;

      X1, X2 : Int;

   begin

      X1 := Int (Calendar.Year  (Now)) * 12 * 31 +

            Int (Calendar.Month (Now)) * 31 +

            Int (Calendar.Day   (Now));

      X2 := Int (Calendar.Seconds (Now) * Duration (1000.0));

      X1 := 2 + X1 mod (K1 - 3);

      X2 := 2 + X2 mod (K2 - 3);

      --  Eliminate visible effects of same day starts

      for J in 1 .. 5 loop

         X1 := Square_Mod_N (X1, K1);

         X2 := Square_Mod_N (X2, K2);

      end loop;

      Genp.all :=

        (X1  => X1,

         X2  => X2,

         P   => K1,

         Q   => K2,

         X   => 1,

         Scl => Scal);

   end Reset;

   ----------

   -- Save --

   ----------

   procedure Save (Gen : Generator; To_State : out State) is

   begin

      To_State := Gen.Gen_State;

   end Save;

   ------------------

   -- Square_Mod_N --

   ------------------

   function Square_Mod_N (X, N : Int) return Int is

      Temp : constant Flt := Flt (X) * Flt (X);

      Div  : Int;

   begin

      Div := Int (Temp / Flt (N));

      Div := Int (Temp - Flt (Div) * Flt (N));

      if Div < 0 then

         return Div + N;

      else

         return Div;

      end if;

   end Square_Mod_N;

   -----------

   -- Value --

   -----------

   function Value (Coded_State : String) return State is

      Last  : constant Natural := Coded_State'Last;

      Start : Positive := Coded_State'First;

      Stop  : Positive := Coded_State'First;

      Outs  : State;

   begin

      while Stop <= Last and then Coded_State (Stop) /= ',' loop

         Stop := Stop + 1;

      end loop;

      if Stop > Last then

         raise Constraint_Error;

      end if;

      Outs.X1 := Int'Value (Coded_State (Start .. Stop - 1));

      Start := Stop + 1;

      loop

         Stop := Stop + 1;

         exit when Stop > Last or else Coded_State (Stop) = ',';

      end loop;

      if Stop > Last then

         raise Constraint_Error;

      end if;

      Outs.X2 := Int'Value (Coded_State (Start .. Stop - 1));

      Start := Stop + 1;

      loop

         Stop := Stop + 1;

         exit when Stop > Last or else Coded_State (Stop) = ',';

      end loop;

      if Stop > Last then

         raise Constraint_Error;

      end if;

      Outs.P   := Int'Value (Coded_State (Start .. Stop - 1));

      Outs.Q   := Int'Value (Coded_State (Stop + 1 .. Last));

      Outs.X   := Euclid (Outs.P, Outs.Q);

      Outs.Scl := 1.0 / (Flt (Outs.P) * Flt (Outs.Q));

      --  Now do *some* sanity checks

      if Outs.Q < 31 or else Outs.P < 31

        or else Outs.X1 not in 2 .. Outs.P - 1

        or else Outs.X2 not in 2 .. Outs.Q - 1

      then

         raise Constraint_Error;

      end if;

      return Outs;

   end Value;

end GNAT.MBBS_Float_Random;