File : g-mbflra.adb
1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT RUN-TIME COMPONENTS --
4 -- --
5 -- G N A T . M B B S _ F L O A T _ R A N D O M --
6 -- --
7 -- B o d y --
8 -- --
9 -- Copyright (C) 1992-2010, Free Software Foundation, Inc. --
10 -- --
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. --
17 -- --
18 -- --
19 -- --
20 -- --
21 -- --
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/>. --
26 -- --
27 -- GNAT was originally developed by the GNAT team at New York University. --
28 -- Extensive contributions were provided by Ada Core Technologies Inc. --
29 -- --
30 ------------------------------------------------------------------------------
31
32 with Ada.Calendar;
33
34 package body GNAT.MBBS_Float_Random is
35
36 -------------------------
37 -- Implementation Note --
38 -------------------------
39
40 -- The design of this spec is a bit 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 would be to add a self-referential component to the generator
44 -- allowing access to the generator object from inside the function. This
45 -- would work because the generator is limited, which prevents any copy.
46
47 -- This is a bit heavy, so what we do is to use Unrestricted_Access to
48 -- get a pointer to the state in the passed Generator. This works because
49 -- Generator is a limited type and will thus always be passed by reference.
50
51 package Calendar renames Ada.Calendar;
52
53 type Pointer is access all State;
54
55 -----------------------
56 -- Local Subprograms --
57 -----------------------
58
59 procedure Euclid (P, Q : Int; X, Y : out Int; GCD : out Int);
60
61 function Euclid (P, Q : Int) return Int;
62
63 function Square_Mod_N (X, N : Int) return Int;
64
65 ------------
66 -- Euclid --
67 ------------
68
69 procedure Euclid (P, Q : Int; X, Y : out Int; GCD : out Int) is
70
71 XT : Int := 1;
72 YT : Int := 0;
73
74 procedure Recur
75 (P, Q : Int; -- a (i-1), a (i)
76 X, Y : Int; -- x (i), y (i)
77 XP, YP : in out Int; -- x (i-1), y (i-1)
78 GCD : out Int);
79
80 procedure Recur
81 (P, Q : Int;
82 X, Y : Int;
83 XP, YP : in out Int;
84 GCD : out Int)
85 is
86 Quo : Int := P / Q; -- q <-- |_ a (i-1) / a (i) _|
87 XT : Int := X; -- x (i)
88 YT : Int := Y; -- y (i)
89
90 begin
91 if P rem Q = 0 then -- while does not divide
92 GCD := Q;
93 XP := X;
94 YP := Y;
95 else
96 Recur (Q, P - Q * Quo, XP - Quo * X, YP - Quo * Y, XT, YT, Quo);
97
98 -- a (i) <== a (i)
99 -- a (i+1) <-- a (i-1) - q*a (i)
100 -- x (i+1) <-- x (i-1) - q*x (i)
101 -- y (i+1) <-- y (i-1) - q*y (i)
102 -- x (i) <== x (i)
103 -- y (i) <== y (i)
104
105 XP := XT;
106 YP := YT;
107 GCD := Quo;
108 end if;
109 end Recur;
110
111 -- Start of processing for Euclid
112
113 begin
114 Recur (P, Q, 0, 1, XT, YT, GCD);
115 X := XT;
116 Y := YT;
117 end Euclid;
118
119 function Euclid (P, Q : Int) return Int is
120 X, Y, GCD : Int;
121 pragma Unreferenced (Y, GCD);
122 begin
123 Euclid (P, Q, X, Y, GCD);
124 return X;
125 end Euclid;
126
127 -----------
128 -- Image --
129 -----------
130
131 function Image (Of_State : State) return String is
132 begin
133 return Int'Image (Of_State.X1) & ',' & Int'Image (Of_State.X2)
134 & ',' &
135 Int'Image (Of_State.P) & ',' & Int'Image (Of_State.Q);
136 end Image;
137
138 ------------
139 -- Random --
140 ------------
141
142 function Random (Gen : Generator) return Uniformly_Distributed is
143 Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
144
145 begin
146 Genp.X1 := Square_Mod_N (Genp.X1, Genp.P);
147 Genp.X2 := Square_Mod_N (Genp.X2, Genp.Q);
148 return
149 Float ((Flt (((Genp.X2 - Genp.X1) * Genp.X)
150 mod Genp.Q) * Flt (Genp.P)
151 + Flt (Genp.X1)) * Genp.Scl);
152 end Random;
153
154 -----------
155 -- Reset --
156 -----------
157
158 -- Version that works from given initiator value
159
160 procedure Reset (Gen : Generator; Initiator : Integer) is
161 Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
162 X1, X2 : Int;
163
164 begin
165 X1 := 2 + Int (Initiator) mod (K1 - 3);
166 X2 := 2 + Int (Initiator) mod (K2 - 3);
167
168 -- Eliminate effects of small initiators
169
170 for J in 1 .. 5 loop
171 X1 := Square_Mod_N (X1, K1);
172 X2 := Square_Mod_N (X2, K2);
173 end loop;
174
175 Genp.all :=
176 (X1 => X1,
177 X2 => X2,
178 P => K1,
179 Q => K2,
180 X => 1,
181 Scl => Scal);
182 end Reset;
183
184 -- Version that works from specific saved state
185
186 procedure Reset (Gen : Generator; From_State : State) is
187 Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
188
189 begin
190 Genp.all := From_State;
191 end Reset;
192
193 -- Version that works from calendar
194
195 procedure Reset (Gen : Generator) is
196 Genp : constant Pointer := Gen.Gen_State'Unrestricted_Access;
197 Now : constant Calendar.Time := Calendar.Clock;
198 X1, X2 : Int;
199
200 begin
201 X1 := Int (Calendar.Year (Now)) * 12 * 31 +
202 Int (Calendar.Month (Now)) * 31 +
203 Int (Calendar.Day (Now));
204
205 X2 := Int (Calendar.Seconds (Now) * Duration (1000.0));
206
207 X1 := 2 + X1 mod (K1 - 3);
208 X2 := 2 + X2 mod (K2 - 3);
209
210 -- Eliminate visible effects of same day starts
211
212 for J in 1 .. 5 loop
213 X1 := Square_Mod_N (X1, K1);
214 X2 := Square_Mod_N (X2, K2);
215 end loop;
216
217 Genp.all :=
218 (X1 => X1,
219 X2 => X2,
220 P => K1,
221 Q => K2,
222 X => 1,
223 Scl => Scal);
224
225 end Reset;
226
227 ----------
228 -- Save --
229 ----------
230
231 procedure Save (Gen : Generator; To_State : out State) is
232 begin
233 To_State := Gen.Gen_State;
234 end Save;
235
236 ------------------
237 -- Square_Mod_N --
238 ------------------
239
240 function Square_Mod_N (X, N : Int) return Int is
241 Temp : constant Flt := Flt (X) * Flt (X);
242 Div : Int;
243
244 begin
245 Div := Int (Temp / Flt (N));
246 Div := Int (Temp - Flt (Div) * Flt (N));
247
248 if Div < 0 then
249 return Div + N;
250 else
251 return Div;
252 end if;
253 end Square_Mod_N;
254
255 -----------
256 -- Value --
257 -----------
258
259 function Value (Coded_State : String) return State is
260 Last : constant Natural := Coded_State'Last;
261 Start : Positive := Coded_State'First;
262 Stop : Positive := Coded_State'First;
263 Outs : State;
264
265 begin
266 while Stop <= Last and then Coded_State (Stop) /= ',' loop
267 Stop := Stop + 1;
268 end loop;
269
270 if Stop > Last then
271 raise Constraint_Error;
272 end if;
273
274 Outs.X1 := Int'Value (Coded_State (Start .. Stop - 1));
275 Start := Stop + 1;
276
277 loop
278 Stop := Stop + 1;
279 exit when Stop > Last or else Coded_State (Stop) = ',';
280 end loop;
281
282 if Stop > Last then
283 raise Constraint_Error;
284 end if;
285
286 Outs.X2 := Int'Value (Coded_State (Start .. Stop - 1));
287 Start := Stop + 1;
288
289 loop
290 Stop := Stop + 1;
291 exit when Stop > Last or else Coded_State (Stop) = ',';
292 end loop;
293
294 if Stop > Last then
295 raise Constraint_Error;
296 end if;
297
298 Outs.P := Int'Value (Coded_State (Start .. Stop - 1));
299 Outs.Q := Int'Value (Coded_State (Stop + 1 .. Last));
300 Outs.X := Euclid (Outs.P, Outs.Q);
301 Outs.Scl := 1.0 / (Flt (Outs.P) * Flt (Outs.Q));
302
303 -- Now do *some* sanity checks
304
305 if Outs.Q < 31 or else Outs.P < 31
306 or else Outs.X1 not in 2 .. Outs.P - 1
307 or else Outs.X2 not in 2 .. Outs.Q - 1
308 then
309 raise Constraint_Error;
310 end if;
311
312 return Outs;
313 end Value;
314 end GNAT.MBBS_Float_Random;