1 ------------------------------------------------------------------------------
3 -- GNAT RUN-TIME 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) 1992-2009, 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 3, 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. --
18 -- As a special exception under Section 7 of GPL version 3, you are granted --
19 -- additional permissions described in the GCC Runtime Library Exception, --
20 -- version 3.1, as published by the Free Software Foundation. --
22 -- You should have received a copy of the GNU General Public License and --
23 -- a copy of the GCC Runtime Library Exception along with this program; --
24 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
25 -- <http://www.gnu.org/licenses/>. --
27 -- GNAT was originally developed by the GNAT team at New York University. --
28 -- Extensive contributions were provided by Ada Core Technologies Inc. --
30 ------------------------------------------------------------------------------
34 package body Ada.Numerics.Float_Random is
36 -------------------------
37 -- Implementation Note --
38 -------------------------
40 -- The design of this spec is very awkward, as a result of Ada 95 not
41 -- permitting in-out parameters for function formals (most naturally
42 -- Generator values would be passed this way). In pure Ada 95, the only
43 -- solution is to use the heap and pointers, and, to avoid memory leaks,
46 -- This is awfully heavy, so what we do is to use Unrestricted_Access to
47 -- get a pointer to the state in the passed Generator. This works because
48 -- Generator is a limited type and will thus always be passed by reference.
50 type Pointer is access all State;
52 -----------------------
53 -- Local Subprograms --
54 -----------------------
56 procedure Euclid (P, Q : Int; X, Y : out Int; GCD : out Int);
58 function Euclid (P, Q : Int) return Int;
60 function Square_Mod_N (X, N : Int) return Int;
66 procedure Euclid (P, Q : Int; X, Y : out Int; GCD : out Int) is
72 (P, Q : Int; -- a (i-1), a (i)
73 X, Y : Int; -- x (i), y (i)
74 XP, YP : in out Int; -- x (i-1), y (i-1)
83 Quo : Int := P / Q; -- q <-- |_ a (i-1) / a (i) _|
84 XT : Int := X; -- x (i)
85 YT : Int := Y; -- y (i)
88 if P rem Q = 0 then -- while does not divide
93 Recur (Q, P - Q * Quo, XP - Quo * X, YP - Quo * Y, XT, YT, Quo);
96 -- a (i+1) <-- a (i-1) - q*a (i)
97 -- x (i+1) <-- x (i-1) - q*x (i)
98 -- y (i+1) <-- y (i-1) - q*y (i)
108 -- Start of processing for Euclid
111 Recur (P, Q, 0, 1, XT, YT, GCD);
116 function Euclid (P, Q : Int) return Int is
118 pragma Unreferenced (Y, GCD);
120 Euclid (P, Q, X, Y, GCD);
128 function Image (Of_State : State) return String is
130 return Int'Image (Of_State.X1) & ',' & Int'Image (Of_State.X2)
132 Int'Image (Of_State.P) & ',' & Int'Image (Of_State.Q);
139 function Random (Gen : Generator) return Uniformly_Distributed is
140 Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
143 Genp.X1 := Square_Mod_N (Genp.X1, Genp.P);
144 Genp.X2 := Square_Mod_N (Genp.X2, Genp.Q);
146 Float ((Flt (((Genp.X2 - Genp.X1) * Genp.X)
147 mod Genp.Q) * Flt (Genp.P)
148 + Flt (Genp.X1)) * Genp.Scl);
155 -- Version that works from given initiator value
157 procedure Reset (Gen : Generator; Initiator : Integer) is
158 Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
162 X1 := 2 + Int (Initiator) mod (K1 - 3);
163 X2 := 2 + Int (Initiator) mod (K2 - 3);
165 -- Eliminate effects of small initiators
168 X1 := Square_Mod_N (X1, K1);
169 X2 := Square_Mod_N (X2, K2);
181 -- Version that works from specific saved state
183 procedure Reset (Gen : Generator; From_State : State) is
184 Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
187 Genp.all := From_State;
190 -- Version that works from calendar
192 procedure Reset (Gen : Generator) is
193 Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
194 Now : constant Calendar.Time := Calendar.Clock;
198 X1 := Int (Calendar.Year (Now)) * 12 * 31 +
199 Int (Calendar.Month (Now)) * 31 +
200 Int (Calendar.Day (Now));
202 X2 := Int (Calendar.Seconds (Now) * Duration (1000.0));
204 X1 := 2 + X1 mod (K1 - 3);
205 X2 := 2 + X2 mod (K2 - 3);
207 -- Eliminate visible effects of same day starts
210 X1 := Square_Mod_N (X1, K1);
211 X2 := Square_Mod_N (X2, K2);
228 procedure Save (Gen : Generator; To_State : out State) is
230 To_State := Gen.Gen_State;
237 function Square_Mod_N (X, N : Int) return Int is
238 Temp : constant Flt := Flt (X) * Flt (X);
242 Div := Int (Temp / Flt (N));
243 Div := Int (Temp - Flt (Div) * Flt (N));
256 function Value (Coded_State : String) return State is
257 Last : constant Natural := Coded_State'Last;
258 Start : Positive := Coded_State'First;
259 Stop : Positive := Coded_State'First;
263 while Stop <= Last and then Coded_State (Stop) /= ',' loop
268 raise Constraint_Error;
271 Outs.X1 := Int'Value (Coded_State (Start .. Stop - 1));
276 exit when Stop > Last or else Coded_State (Stop) = ',';
280 raise Constraint_Error;
283 Outs.X2 := Int'Value (Coded_State (Start .. Stop - 1));
288 exit when Stop > Last or else Coded_State (Stop) = ',';
292 raise Constraint_Error;
295 Outs.P := Int'Value (Coded_State (Start .. Stop - 1));
296 Outs.Q := Int'Value (Coded_State (Stop + 1 .. Last));
297 Outs.X := Euclid (Outs.P, Outs.Q);
298 Outs.Scl := 1.0 / (Flt (Outs.P) * Flt (Outs.Q));
300 -- Now do *some* sanity checks
302 if Outs.Q < 31 or else Outs.P < 31
303 or else Outs.X1 not in 2 .. Outs.P - 1
304 or else Outs.X2 not in 2 .. Outs.Q - 1
306 raise Constraint_Error;
311 end Ada.Numerics.Float_Random;