------------------------------------------------------------------------------ -- -- -- 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 -- -- -- -- Copyright (C) 1992-2003 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; -- Set if we need more than 32 bits in the result. In practice we will -- only use the meaningful 48 bits of any 64 bit number generated, since -- if more than 48 bits are required, we split the computation into two -- separate parts, since the algorithm does not behave above 48 bits. ----------------------- -- 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 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)); Outs.Q := Int'Value (Coded_State (Stop + 1 .. 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;