1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
|
------------------------------------------------------------------------------
-- --
-- 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 --
-- --
-- $Revision: 1.1 $
-- --
-- Copyright (C) 1992-1999 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;
-----------------------
-- 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;
|
