------------------------------------------------------------------------------ | |

-- -- | |

-- 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 | |

Start : Positive := Coded_State'First; | |

Stop : Positive := Coded_State'First; | |

Outs : State; | |

begin | |

while Coded_State (Stop) /= ',' loop | |

Stop := Stop + 1; | |

end loop; | |

Outs.X1 := Int'Value (Coded_State (Start .. Stop - 1)); | |

Start := Stop + 1; | |

loop | |

Stop := Stop + 1; | |

exit when Coded_State (Stop) = ','; | |

end loop; | |

Outs.X2 := Int'Value (Coded_State (Start .. Stop - 1)); | |

Outs.Q := Int'Value (Coded_State (Stop + 1 .. Coded_State'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; |