1 ------------------------------------------------------------------------------
3 -- GNAT RUNTIME COMPONENTS --
5 -- A D A . N U M E R I C S . F L O A T _ R A N D O M --
9 -- Copyright (C) 1992-2002, Free Software Foundation, Inc. --
11 -- GNAT is free software; you can redistribute it and/or modify it under --
12 -- terms of the GNU General Public License as published by the Free Soft- --
13 -- ware Foundation; either version 2, or (at your option) any later ver- --
14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
16 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
17 -- for more details. You should have received a copy of the GNU General --
18 -- Public License distributed with GNAT; see file COPYING. If not, write --
19 -- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
20 -- MA 02111-1307, USA. --
22 -- As a special exception, if other files instantiate generics from this --
23 -- unit, or you link this unit with other files to produce an executable, --
24 -- this unit does not by itself cause the resulting executable to be --
25 -- covered by the GNU General Public License. This exception does not --
26 -- however invalidate any other reasons why the executable file might be --
27 -- covered by the GNU Public License. --
29 -- GNAT was originally developed by the GNAT team at New York University. --
30 -- Extensive contributions were provided by Ada Core Technologies Inc. --
32 ------------------------------------------------------------------------------
36 package body Ada.Numerics.Float_Random is
38 -------------------------
39 -- Implementation Note --
40 -------------------------
42 -- The design of this spec is very awkward, as a result of Ada 95 not
43 -- permitting in-out parameters for function formals (most naturally
44 -- Generator values would be passed this way). In pure Ada 95, the only
45 -- solution is to use the heap and pointers, and, to avoid memory leaks,
48 -- This is awfully heavy, so what we do is to use Unrestricted_Access to
49 -- get a pointer to the state in the passed Generator. This works because
50 -- Generator is a limited type and will thus always be passed by reference.
52 type Pointer is access all State;
54 -----------------------
55 -- Local Subprograms --
56 -----------------------
58 procedure Euclid (P, Q : in Int; X, Y : out Int; GCD : out Int);
60 function Euclid (P, Q : Int) return Int;
62 function Square_Mod_N (X, N : Int) return Int;
68 procedure Euclid (P, Q : in Int; X, Y : out Int; GCD : out Int) is
74 (P, Q : in Int; -- a (i-1), a (i)
75 X, Y : in Int; -- x (i), y (i)
76 XP, YP : in out Int; -- x (i-1), y (i-1)
85 Quo : Int := P / Q; -- q <-- |_ a (i-1) / a (i) _|
86 XT : Int := X; -- x (i)
87 YT : Int := Y; -- y (i)
90 if P rem Q = 0 then -- while does not divide
95 Recur (Q, P - Q * Quo, XP - Quo * X, YP - Quo * Y, XT, YT, Quo);
98 -- a (i+1) <-- a (i-1) - q*a (i)
99 -- x (i+1) <-- x (i-1) - q*x (i)
100 -- y (i+1) <-- y (i-1) - q*y (i)
110 -- Start of processing for Euclid
113 Recur (P, Q, 0, 1, XT, YT, GCD);
118 function Euclid (P, Q : Int) return Int is
122 Euclid (P, Q, X, Y, GCD);
130 function Image (Of_State : State) return String is
132 return Int'Image (Of_State.X1) & ',' & Int'Image (Of_State.X2)
134 Int'Image (Of_State.P) & ',' & Int'Image (Of_State.Q);
141 function Random (Gen : Generator) return Uniformly_Distributed is
142 Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
145 Genp.X1 := Square_Mod_N (Genp.X1, Genp.P);
146 Genp.X2 := Square_Mod_N (Genp.X2, Genp.Q);
148 Float ((Flt (((Genp.X2 - Genp.X1) * Genp.X)
149 mod Genp.Q) * Flt (Genp.P)
150 + Flt (Genp.X1)) * Genp.Scl);
157 -- Version that works from given initiator value
159 procedure Reset (Gen : in Generator; Initiator : in Integer) is
160 Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
164 X1 := 2 + Int (Initiator) mod (K1 - 3);
165 X2 := 2 + Int (Initiator) mod (K2 - 3);
167 -- Eliminate effects of small Initiators.
170 X1 := Square_Mod_N (X1, K1);
171 X2 := Square_Mod_N (X2, K2);
183 -- Version that works from specific saved state
185 procedure Reset (Gen : Generator; From_State : State) is
186 Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
189 Genp.all := From_State;
192 -- Version that works from calendar
194 procedure Reset (Gen : Generator) is
195 Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
196 Now : constant Calendar.Time := Calendar.Clock;
200 X1 := Int (Calendar.Year (Now)) * 12 * 31 +
201 Int (Calendar.Month (Now)) * 31 +
202 Int (Calendar.Day (Now));
204 X2 := Int (Calendar.Seconds (Now) * Duration (1000.0));
206 X1 := 2 + X1 mod (K1 - 3);
207 X2 := 2 + X2 mod (K2 - 3);
209 -- Eliminate visible effects of same day starts
212 X1 := Square_Mod_N (X1, K1);
213 X2 := Square_Mod_N (X2, K2);
230 procedure Save (Gen : in Generator; To_State : out State) is
232 To_State := Gen.Gen_State;
239 function Square_Mod_N (X, N : Int) return Int is
240 Temp : constant Flt := Flt (X) * Flt (X);
244 Div := Int (Temp / Flt (N));
245 Div := Int (Temp - Flt (Div) * Flt (N));
258 function Value (Coded_State : String) return State is
259 Start : Positive := Coded_State'First;
260 Stop : Positive := Coded_State'First;
264 while Coded_State (Stop) /= ',' loop
268 Outs.X1 := Int'Value (Coded_State (Start .. Stop - 1));
273 exit when Coded_State (Stop) = ',';
276 Outs.X2 := Int'Value (Coded_State (Start .. Stop - 1));
281 exit when Coded_State (Stop) = ',';
284 Outs.P := Int'Value (Coded_State (Start .. Stop - 1));
285 Outs.Q := Int'Value (Coded_State (Stop + 1 .. Coded_State'Last));
286 Outs.X := Euclid (Outs.P, Outs.Q);
287 Outs.Scl := 1.0 / (Flt (Outs.P) * Flt (Outs.Q));
289 -- Now do *some* sanity checks.
291 if Outs.Q < 31 or else Outs.P < 31
292 or else Outs.X1 not in 2 .. Outs.P - 1
293 or else Outs.X2 not in 2 .. Outs.Q - 1
295 raise Constraint_Error;
300 end Ada.Numerics.Float_Random;