------------------------------------------------------------------------------
-- --
--- GNAT RUNTIME COMPONENTS --
+-- GNAT RUN-TIME 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) 1992-1999 Free Software Foundation, Inc. --
+-- Copyright (C) 1992-2009, 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- --
+-- 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. 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. --
+-- or FITNESS FOR A PARTICULAR PURPOSE. --
-- --
--- 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. --
+-- 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 Ada.Numerics.Discrete_Random is
type Pointer is access all State;
- Need_64 : constant Boolean := Rst'Pos (Rst'Last) > Int'Last;
+ 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 expresion 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 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;
Temp := Temp + Genp.Q;
end if;
- TF := Offs + (Flt (Temp) * Flt (Genp.P) + Flt (Genp.X1)) * Genp.Scl;
+ 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.
if TF >= Flt (Rst'Pos (Rst'Last)) + 0.5 then
return Rst'First;
- elsif Need_64 then
+ elsif not Fits_In_32_Bits then
return Rst'Val (Interfaces.Integer_64 (TF));
else
return Rst'Val (Int (TF));
end if;
-
end Random;
-----------
X2 := Square_Mod_N (X2, K2);
end loop;
- -- eliminate effects of small Initiators.
+ -- Eliminate effects of small Initiators
Genp.all :=
(X1 => X1,
procedure Reset (Gen : Generator; From_State : State) is
Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
-
begin
Genp.all := From_State;
end Reset;
-----------
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 Coded_State (Stop) /= ',' loop
+ 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 Coded_State (Stop) = ',';
+ 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 .. Coded_State'Last));
+ 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.
+ -- Now do *some* sanity checks
if Outs.Q < 31
or else Outs.X1 not in 2 .. Outs.P - 1
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