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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) 1992-2022, 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;
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;
|
