+++ /dev/null
-------------------------------------------------------------------------------
--- --
--- GNAT RUNTIME COMPONENTS --
--- --
--- A D A . N U M E R I C S . D I S C R E T E _ R A N D O M --
--- --
--- B o d y --
--- --
--- $Revision: 1.1.16.1 $
--- --
--- Copyright (C) 1992-1999 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 2, 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. See the GNU General Public License --
--- for more details. You should have received a copy of the GNU General --
--- Public License distributed with GNAT; see file COPYING. If not, write --
--- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
--- MA 02111-1307, USA. --
--- --
--- As a special exception, if other files instantiate generics from this --
--- unit, or you link this unit with other files to produce an executable, --
--- this unit does not by itself cause the resulting executable to be --
--- covered by the GNU General Public License. This exception does not --
--- however invalidate any other reasons why the executable file might be --
--- covered by the GNU Public License. --
--- --
--- GNAT was originally developed by the GNAT team at New York University. --
--- Extensive contributions were provided by Ada Core Technologies Inc. --
--- --
-------------------------------------------------------------------------------
-
-with Ada.Calendar;
-with Interfaces; use Interfaces;
-
-package body Ada.Numerics.Discrete_Random is
-
- -------------------------
- -- Implementation Note --
- -------------------------
-
- -- The design of this spec is very 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 is to use the heap and pointers, and, to avoid memory leaks,
- -- controlled types.
-
- -- This is awfully 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.
-
- type Pointer is access all State;
-
- Need_64 : constant Boolean := Rst'Pos (Rst'Last) > Int'Last;
-
- -----------------------
- -- Local Subprograms --
- -----------------------
-
- function Square_Mod_N (X, N : Int) return Int;
- pragma Inline (Square_Mod_N);
- -- Computes X**2 mod N avoiding intermediate overflow
-
- -----------
- -- 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.Q);
- end Image;
-
- ------------
- -- Random --
- ------------
-
- function Random (Gen : Generator) return Rst is
- Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
- Temp : Int;
- TF : Flt;
-
- begin
- -- Check for flat range here, since we are typically run with checks
- -- off, note that in practice, this condition will usually be static
- -- so we will not actually generate any code for the normal case.
-
- if Rst'Last < Rst'First then
- raise Constraint_Error;
- end if;
-
- -- Continue with computation if non-flat range
-
- Genp.X1 := Square_Mod_N (Genp.X1, Genp.P);
- Genp.X2 := Square_Mod_N (Genp.X2, Genp.Q);
- Temp := Genp.X2 - Genp.X1;
-
- -- Following duplication is not an error, it is a loop unwinding!
-
- if Temp < 0 then
- Temp := Temp + Genp.Q;
- end if;
-
- if Temp < 0 then
- Temp := Temp + Genp.Q;
- end if;
-
- TF := Offs + (Flt (Temp) * Flt (Genp.P) + Flt (Genp.X1)) * Genp.Scl;
-
- -- Pathological, but there do exist cases where the rounding implicit
- -- in calculating the scale factor will cause rounding to 'Last + 1.
- -- In those cases, returning 'First results in the least bias.
-
- if TF >= Flt (Rst'Pos (Rst'Last)) + 0.5 then
- return Rst'First;
-
- elsif Need_64 then
- return Rst'Val (Interfaces.Integer_64 (TF));
-
- else
- return Rst'Val (Int (TF));
- end if;
-
- end Random;
-
- -----------
- -- Reset --
- -----------
-
- 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);
-
- for J in 1 .. 5 loop
- X1 := Square_Mod_N (X1, K1);
- X2 := Square_Mod_N (X2, K2);
- end loop;
-
- -- eliminate effects of small Initiators.
-
- Genp.all :=
- (X1 => X1,
- X2 => X2,
- P => K1,
- Q => K2,
- FP => K1F,
- Scl => Scal);
- end Reset;
-
- -----------
- -- Reset --
- -----------
-
- procedure Reset (Gen : Generator) is
- Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
- Now : constant Calendar.Time := Calendar.Clock;
- X1 : Int;
- 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,
- FP => K1F,
- Scl => Scal);
-
- end Reset;
-
- -----------
- -- Reset --
- -----------
-
- procedure Reset (Gen : Generator; From_State : State) is
- Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
-
- begin
- Genp.all := From_State;
- 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
- begin
- return Int ((Integer_64 (X) ** 2) mod (Integer_64 (N)));
- end Square_Mod_N;
-
- -----------
- -- Value --
- -----------
-
- function Value (Coded_State : String) return State is
- Start : Positive := Coded_State'First;
- Stop : Positive := Coded_State'First;
- Outs : State;
-
- begin
- while Coded_State (Stop) /= ',' loop
- Stop := Stop + 1;
- end loop;
-
- Outs.X1 := Int'Value (Coded_State (Start .. Stop - 1));
- Start := Stop + 1;
-
- loop
- Stop := Stop + 1;
- exit when Coded_State (Stop) = ',';
- end loop;
-
- Outs.X2 := Int'Value (Coded_State (Start .. Stop - 1));
- Outs.Q := Int'Value (Coded_State (Stop + 1 .. Coded_State'Last));
- Outs.P := Outs.Q * 2 + 1;
- Outs.FP := Flt (Outs.P);
- Outs.Scl := (RstL - RstF + 1.0) / (Flt (Outs.P) * Flt (Outs.Q));
-
- -- Now do *some* sanity checks.
-
- if Outs.Q < 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 Ada.Numerics.Discrete_Random;
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