| ------------------------------------------------------------------------------ |
| -- -- |
| -- GNAT RUN-TIME COMPONENTS -- |
| -- -- |
| -- G N A T . M B B S _ D I S C R E T E _ R A N D O M -- |
| -- -- |
| -- B o d y -- |
| -- -- |
| -- Copyright (C) 1992-2021, 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; |
| |
| with Interfaces; use Interfaces; |
| |
| package body GNAT.MBBS_Discrete_Random is |
| |
| package Calendar renames Ada.Calendar; |
| |
| Fits_In_32_Bits : constant Boolean := |
| Rst'Size < 31 |
| or else (Rst'Size = 31 |
| and then Rst'Pos (Rst'First) < 0); |
| -- This is set True if we do not need more than 32 bits in the result. If |
| -- we need 64-bits, 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. |
| |
| -- The way this expression works is that obviously if the size is 31 bits, |
| -- it fits in 32 bits. In the 32-bit case, it fits in 32-bit signed if the |
| -- range has negative values. It is too conservative in the case that the |
| -- programmer has set a size greater than the default, e.g. a size of 33 |
| -- for an integer type with a range of 1..10, but an over-conservative |
| -- result is OK. The important thing is that the value is only True if |
| -- we know the result will fit in 32-bits signed. If the value is False |
| -- when it could be True, the behavior will be correct, just a bit less |
| -- efficient than it could have been in some unusual cases. |
| -- |
| -- One might assume that we could get a more accurate result by testing |
| -- the lower and upper bounds of the type Rst against the bounds of 32-bit |
| -- Integer. However, there is no easy way to do that. Why? Because in the |
| -- relatively rare case where this expression has to be evaluated at run |
| -- time rather than compile time (when the bounds are dynamic), we need a |
| -- type to use for the computation. But the possible range of upper bound |
| -- values for Rst (remembering the possibility of 64-bit modular types) is |
| -- from -2**63 to 2**64-1, and no run-time type has a big enough range. |
| |
| ----------------------- |
| -- 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 |
| S : State renames Gen.Writable.Self.Gen_State; |
| 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 |
| |
| S.X1 := Square_Mod_N (S.X1, S.P); |
| S.X2 := Square_Mod_N (S.X2, S.Q); |
| Temp := S.X2 - S.X1; |
| |
| -- Following duplication is not an error, it is a loop unwinding |
| |
| if Temp < 0 then |
| Temp := Temp + S.Q; |
| end if; |
| |
| if Temp < 0 then |
| Temp := Temp + S.Q; |
| end if; |
| |
| TF := Offs + (Flt (Temp) * Flt (S.P) + Flt (S.X1)) * S.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 not Fits_In_32_Bits 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 |
| S : State renames Gen.Writable.Self.Gen_State; |
| 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 |
| |
| S := |
| (X1 => X1, |
| X2 => X2, |
| P => K1, |
| Q => K2, |
| FP => K1F, |
| Scl => Scal); |
| end Reset; |
| |
| ----------- |
| -- Reset -- |
| ----------- |
| |
| procedure Reset (Gen : Generator) is |
| S : State renames Gen.Writable.Self.Gen_State; |
| 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; |
| |
| S := |
| (X1 => X1, |
| X2 => X2, |
| P => K1, |
| Q => K2, |
| FP => K1F, |
| Scl => Scal); |
| |
| end Reset; |
| |
| ----------- |
| -- Reset -- |
| ----------- |
| |
| procedure Reset (Gen : Generator; From_State : State) is |
| begin |
| Gen.Writable.Self.Gen_State := 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 GNAT.MBBS_Discrete_Random; |
