------------------------------------------------------------------------------ -- -- -- 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) 1992-2024, 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 -- -- . -- -- -- -- 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;