1 ------------------------------------------------------------------------------
3 -- GNAT RUNTIME COMPONENTS --
5 -- 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 --
10 -- Copyright (C) 1992-1999 Free Software Foundation, Inc. --
12 -- GNAT is free software; you can redistribute it and/or modify it under --
13 -- terms of the GNU General Public License as published by the Free Soft- --
14 -- ware Foundation; either version 2, or (at your option) any later ver- --
15 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
16 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
17 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
18 -- for more details. You should have received a copy of the GNU General --
19 -- Public License distributed with GNAT; see file COPYING. If not, write --
20 -- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
21 -- MA 02111-1307, USA. --
23 -- As a special exception, if other files instantiate generics from this --
24 -- unit, or you link this unit with other files to produce an executable, --
25 -- this unit does not by itself cause the resulting executable to be --
26 -- covered by the GNU General Public License. This exception does not --
27 -- however invalidate any other reasons why the executable file might be --
28 -- covered by the GNU Public License. --
30 -- GNAT was originally developed by the GNAT team at New York University. --
31 -- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
33 ------------------------------------------------------------------------------
36 with Interfaces
; use Interfaces
;
38 package body Ada
.Numerics
.Discrete_Random
is
40 -------------------------
41 -- Implementation Note --
42 -------------------------
44 -- The design of this spec is very awkward, as a result of Ada 95 not
45 -- permitting in-out parameters for function formals (most naturally
46 -- Generator values would be passed this way). In pure Ada 95, the only
47 -- solution is to use the heap and pointers, and, to avoid memory leaks,
50 -- This is awfully heavy, so what we do is to use Unrestricted_Access to
51 -- get a pointer to the state in the passed Generator. This works because
52 -- Generator is a limited type and will thus always be passed by reference.
54 type Pointer
is access all State
;
56 Need_64
: constant Boolean := Rst
'Pos (Rst
'Last) > Int
'Last;
58 -----------------------
59 -- Local Subprograms --
60 -----------------------
62 function Square_Mod_N
(X
, N
: Int
) return Int
;
63 pragma Inline
(Square_Mod_N
);
64 -- Computes X**2 mod N avoiding intermediate overflow
70 function Image
(Of_State
: State
) return String is
72 return Int
'Image (Of_State
.X1
) &
74 Int
'Image (Of_State
.X2
) &
76 Int
'Image (Of_State
.Q
);
83 function Random
(Gen
: Generator
) return Rst
is
84 Genp
: constant Pointer
:= Gen
.Gen_State
'Unrestricted_Access;
89 -- Check for flat range here, since we are typically run with checks
90 -- off, note that in practice, this condition will usually be static
91 -- so we will not actually generate any code for the normal case.
93 if Rst
'Last < Rst
'First then
94 raise Constraint_Error
;
97 -- Continue with computation if non-flat range
99 Genp
.X1
:= Square_Mod_N
(Genp
.X1
, Genp
.P
);
100 Genp
.X2
:= Square_Mod_N
(Genp
.X2
, Genp
.Q
);
101 Temp
:= Genp
.X2
- Genp
.X1
;
103 -- Following duplication is not an error, it is a loop unwinding!
106 Temp
:= Temp
+ Genp
.Q
;
110 Temp
:= Temp
+ Genp
.Q
;
113 TF
:= Offs
+ (Flt
(Temp
) * Flt
(Genp
.P
) + Flt
(Genp
.X1
)) * Genp
.Scl
;
115 -- Pathological, but there do exist cases where the rounding implicit
116 -- in calculating the scale factor will cause rounding to 'Last + 1.
117 -- In those cases, returning 'First results in the least bias.
119 if TF
>= Flt
(Rst
'Pos (Rst
'Last)) + 0.5 then
123 return Rst
'Val (Interfaces
.Integer_64
(TF
));
126 return Rst
'Val (Int
(TF
));
135 procedure Reset
(Gen
: Generator
; Initiator
: Integer) is
136 Genp
: constant Pointer
:= Gen
.Gen_State
'Unrestricted_Access;
140 X1
:= 2 + Int
(Initiator
) mod (K1
- 3);
141 X2
:= 2 + Int
(Initiator
) mod (K2
- 3);
144 X1
:= Square_Mod_N
(X1
, K1
);
145 X2
:= Square_Mod_N
(X2
, K2
);
148 -- eliminate effects of small Initiators.
163 procedure Reset
(Gen
: Generator
) is
164 Genp
: constant Pointer
:= Gen
.Gen_State
'Unrestricted_Access;
165 Now
: constant Calendar
.Time
:= Calendar
.Clock
;
170 X1
:= Int
(Calendar
.Year
(Now
)) * 12 * 31 +
171 Int
(Calendar
.Month
(Now
) * 31) +
172 Int
(Calendar
.Day
(Now
));
174 X2
:= Int
(Calendar
.Seconds
(Now
) * Duration (1000.0));
176 X1
:= 2 + X1
mod (K1
- 3);
177 X2
:= 2 + X2
mod (K2
- 3);
179 -- Eliminate visible effects of same day starts
182 X1
:= Square_Mod_N
(X1
, K1
);
183 X2
:= Square_Mod_N
(X2
, K2
);
200 procedure Reset
(Gen
: Generator
; From_State
: State
) is
201 Genp
: constant Pointer
:= Gen
.Gen_State
'Unrestricted_Access;
204 Genp
.all := From_State
;
211 procedure Save
(Gen
: Generator
; To_State
: out State
) is
213 To_State
:= Gen
.Gen_State
;
220 function Square_Mod_N
(X
, N
: Int
) return Int
is
222 return Int
((Integer_64
(X
) ** 2) mod (Integer_64
(N
)));
229 function Value
(Coded_State
: String) return State
is
230 Start
: Positive := Coded_State
'First;
231 Stop
: Positive := Coded_State
'First;
235 while Coded_State
(Stop
) /= ',' loop
239 Outs
.X1
:= Int
'Value (Coded_State
(Start
.. Stop
- 1));
244 exit when Coded_State
(Stop
) = ',';
247 Outs
.X2
:= Int
'Value (Coded_State
(Start
.. Stop
- 1));
248 Outs
.Q
:= Int
'Value (Coded_State
(Stop
+ 1 .. Coded_State
'Last));
249 Outs
.P
:= Outs
.Q
* 2 + 1;
250 Outs
.FP
:= Flt
(Outs
.P
);
251 Outs
.Scl
:= (RstL
- RstF
+ 1.0) / (Flt
(Outs
.P
) * Flt
(Outs
.Q
));
253 -- Now do *some* sanity checks.
256 or else Outs
.X1
not in 2 .. Outs
.P
- 1
257 or else Outs
.X2
not in 2 .. Outs
.Q
- 1
259 raise Constraint_Error
;
265 end Ada
.Numerics
.Discrete_Random
;