| ------------------------------------------------------------------------------ |
| -- -- |
| -- 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; |
