2001-10-02 15:55:47 +02:00
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------------------------------------------------------------------------------
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-- --
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-- GNAT RUNTIME COMPONENTS --
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-- --
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-- 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 --
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-- --
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-- B o d y --
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-- --
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-- Copyright (C) 1992-1999 Free Software Foundation, Inc. --
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-- --
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-- GNAT is free software; you can redistribute it and/or modify it under --
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-- terms of the GNU General Public License as published by the Free Soft- --
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-- ware Foundation; either version 2, or (at your option) any later ver- --
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-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
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-- for more details. You should have received a copy of the GNU General --
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-- Public License distributed with GNAT; see file COPYING. If not, write --
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-- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
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-- MA 02111-1307, USA. --
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-- --
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-- As a special exception, if other files instantiate generics from this --
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-- unit, or you link this unit with other files to produce an executable, --
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-- this unit does not by itself cause the resulting executable to be --
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-- covered by the GNU General Public License. This exception does not --
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-- however invalidate any other reasons why the executable file might be --
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-- covered by the GNU Public License. --
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-- --
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-- GNAT was originally developed by the GNAT team at New York University. --
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2002-10-23 09:33:35 +02:00
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-- Extensive contributions were provided by Ada Core Technologies Inc. --
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2001-10-02 15:55:47 +02:00
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-- --
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------------------------------------------------------------------------------
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with Ada.Calendar;
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with Interfaces; use Interfaces;
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package body Ada.Numerics.Discrete_Random is
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-------------------------
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-- Implementation Note --
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-------------------------
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-- The design of this spec is very awkward, as a result of Ada 95 not
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-- permitting in-out parameters for function formals (most naturally
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-- Generator values would be passed this way). In pure Ada 95, the only
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-- solution is to use the heap and pointers, and, to avoid memory leaks,
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-- controlled types.
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-- This is awfully heavy, so what we do is to use Unrestricted_Access to
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-- get a pointer to the state in the passed Generator. This works because
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-- Generator is a limited type and will thus always be passed by reference.
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type Pointer is access all State;
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Need_64 : constant Boolean := Rst'Pos (Rst'Last) > Int'Last;
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-----------------------
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-- Local Subprograms --
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-----------------------
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function Square_Mod_N (X, N : Int) return Int;
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pragma Inline (Square_Mod_N);
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-- Computes X**2 mod N avoiding intermediate overflow
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-----------
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-- Image --
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-----------
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function Image (Of_State : State) return String is
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begin
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return Int'Image (Of_State.X1) &
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',' &
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Int'Image (Of_State.X2) &
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',' &
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Int'Image (Of_State.Q);
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end Image;
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------------
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-- Random --
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------------
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function Random (Gen : Generator) return Rst is
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Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
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Temp : Int;
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TF : Flt;
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begin
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-- Check for flat range here, since we are typically run with checks
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-- off, note that in practice, this condition will usually be static
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-- so we will not actually generate any code for the normal case.
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if Rst'Last < Rst'First then
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raise Constraint_Error;
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end if;
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-- Continue with computation if non-flat range
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Genp.X1 := Square_Mod_N (Genp.X1, Genp.P);
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Genp.X2 := Square_Mod_N (Genp.X2, Genp.Q);
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Temp := Genp.X2 - Genp.X1;
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-- Following duplication is not an error, it is a loop unwinding!
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if Temp < 0 then
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Temp := Temp + Genp.Q;
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end if;
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if Temp < 0 then
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Temp := Temp + Genp.Q;
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end if;
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TF := Offs + (Flt (Temp) * Flt (Genp.P) + Flt (Genp.X1)) * Genp.Scl;
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-- Pathological, but there do exist cases where the rounding implicit
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-- in calculating the scale factor will cause rounding to 'Last + 1.
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-- In those cases, returning 'First results in the least bias.
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if TF >= Flt (Rst'Pos (Rst'Last)) + 0.5 then
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return Rst'First;
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elsif Need_64 then
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return Rst'Val (Interfaces.Integer_64 (TF));
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else
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return Rst'Val (Int (TF));
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end if;
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end Random;
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-----------
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-- Reset --
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-----------
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procedure Reset (Gen : Generator; Initiator : Integer) is
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Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
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X1, X2 : Int;
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begin
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X1 := 2 + Int (Initiator) mod (K1 - 3);
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X2 := 2 + Int (Initiator) mod (K2 - 3);
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for J in 1 .. 5 loop
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X1 := Square_Mod_N (X1, K1);
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X2 := Square_Mod_N (X2, K2);
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end loop;
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-- eliminate effects of small Initiators.
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Genp.all :=
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(X1 => X1,
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X2 => X2,
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P => K1,
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Q => K2,
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FP => K1F,
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Scl => Scal);
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end Reset;
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-----------
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-- Reset --
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-----------
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procedure Reset (Gen : Generator) is
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Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
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Now : constant Calendar.Time := Calendar.Clock;
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X1 : Int;
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X2 : Int;
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begin
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X1 := Int (Calendar.Year (Now)) * 12 * 31 +
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Int (Calendar.Month (Now) * 31) +
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Int (Calendar.Day (Now));
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X2 := Int (Calendar.Seconds (Now) * Duration (1000.0));
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X1 := 2 + X1 mod (K1 - 3);
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X2 := 2 + X2 mod (K2 - 3);
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-- Eliminate visible effects of same day starts
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for J in 1 .. 5 loop
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X1 := Square_Mod_N (X1, K1);
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X2 := Square_Mod_N (X2, K2);
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end loop;
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Genp.all :=
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(X1 => X1,
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X2 => X2,
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P => K1,
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Q => K2,
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FP => K1F,
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Scl => Scal);
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end Reset;
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-----------
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-- Reset --
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-----------
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procedure Reset (Gen : Generator; From_State : State) is
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Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
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begin
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Genp.all := From_State;
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end Reset;
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----------
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-- Save --
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----------
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procedure Save (Gen : Generator; To_State : out State) is
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begin
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To_State := Gen.Gen_State;
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end Save;
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------------------
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-- Square_Mod_N --
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------------------
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function Square_Mod_N (X, N : Int) return Int is
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begin
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return Int ((Integer_64 (X) ** 2) mod (Integer_64 (N)));
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end Square_Mod_N;
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-----------
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-- Value --
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-----------
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function Value (Coded_State : String) return State is
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Start : Positive := Coded_State'First;
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Stop : Positive := Coded_State'First;
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Outs : State;
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begin
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while Coded_State (Stop) /= ',' loop
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Stop := Stop + 1;
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end loop;
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Outs.X1 := Int'Value (Coded_State (Start .. Stop - 1));
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Start := Stop + 1;
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loop
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Stop := Stop + 1;
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exit when Coded_State (Stop) = ',';
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end loop;
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Outs.X2 := Int'Value (Coded_State (Start .. Stop - 1));
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Outs.Q := Int'Value (Coded_State (Stop + 1 .. Coded_State'Last));
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Outs.P := Outs.Q * 2 + 1;
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Outs.FP := Flt (Outs.P);
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Outs.Scl := (RstL - RstF + 1.0) / (Flt (Outs.P) * Flt (Outs.Q));
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-- Now do *some* sanity checks.
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if Outs.Q < 31
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or else Outs.X1 not in 2 .. Outs.P - 1
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or else Outs.X2 not in 2 .. Outs.Q - 1
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then
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raise Constraint_Error;
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end if;
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return Outs;
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end Value;
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end Ada.Numerics.Discrete_Random;
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