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 --
11 -- Copyright (C) 1992-1999 Free Software Foundation, Inc. --
13 -- GNAT is free software; you can redistribute it and/or modify it under --
14 -- terms of the GNU General Public License as published by the Free Soft- --
15 -- ware Foundation; either version 2, or (at your option) any later ver- --
16 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
17 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
18 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
19 -- for more details. You should have received a copy of the GNU General --
20 -- Public License distributed with GNAT; see file COPYING. If not, write --
21 -- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
22 -- MA 02111-1307, USA. --
24 -- As a special exception, if other files instantiate generics from this --
25 -- unit, or you link this unit with other files to produce an executable, --
26 -- this unit does not by itself cause the resulting executable to be --
27 -- covered by the GNU General Public License. This exception does not --
28 -- however invalidate any other reasons why the executable file might be --
29 -- covered by the GNU Public License. --
31 -- GNAT was originally developed by the GNAT team at New York University. --
32 -- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
34 ------------------------------------------------------------------------------
37 with Interfaces
; use Interfaces
;
39 package body Ada
.Numerics
.Discrete_Random
is
41 -------------------------
42 -- Implementation Note --
43 -------------------------
45 -- The design of this spec is very awkward, as a result of Ada 95 not
46 -- permitting in-out parameters for function formals (most naturally
47 -- Generator values would be passed this way). In pure Ada 95, the only
48 -- solution is to use the heap and pointers, and, to avoid memory leaks,
51 -- This is awfully heavy, so what we do is to use Unrestricted_Access to
52 -- get a pointer to the state in the passed Generator. This works because
53 -- Generator is a limited type and will thus always be passed by reference.
55 type Pointer
is access all State
;
57 Need_64
: constant Boolean := Rst
'Pos (Rst
'Last) > Int
'Last;
59 -----------------------
60 -- Local Subprograms --
61 -----------------------
63 function Square_Mod_N
(X
, N
: Int
) return Int
;
64 pragma Inline
(Square_Mod_N
);
65 -- Computes X**2 mod N avoiding intermediate overflow
71 function Image
(Of_State
: State
) return String is
73 return Int
'Image (Of_State
.X1
) &
75 Int
'Image (Of_State
.X2
) &
77 Int
'Image (Of_State
.Q
);
84 function Random
(Gen
: Generator
) return Rst
is
85 Genp
: constant Pointer
:= Gen
.Gen_State
'Unrestricted_Access;
90 -- Check for flat range here, since we are typically run with checks
91 -- off, note that in practice, this condition will usually be static
92 -- so we will not actually generate any code for the normal case.
94 if Rst
'Last < Rst
'First then
95 raise Constraint_Error
;
98 -- Continue with computation if non-flat range
100 Genp
.X1
:= Square_Mod_N
(Genp
.X1
, Genp
.P
);
101 Genp
.X2
:= Square_Mod_N
(Genp
.X2
, Genp
.Q
);
102 Temp
:= Genp
.X2
- Genp
.X1
;
104 -- Following duplication is not an error, it is a loop unwinding!
107 Temp
:= Temp
+ Genp
.Q
;
111 Temp
:= Temp
+ Genp
.Q
;
114 TF
:= Offs
+ (Flt
(Temp
) * Flt
(Genp
.P
) + Flt
(Genp
.X1
)) * Genp
.Scl
;
116 -- Pathological, but there do exist cases where the rounding implicit
117 -- in calculating the scale factor will cause rounding to 'Last + 1.
118 -- In those cases, returning 'First results in the least bias.
120 if TF
>= Flt
(Rst
'Pos (Rst
'Last)) + 0.5 then
124 return Rst
'Val (Interfaces
.Integer_64
(TF
));
127 return Rst
'Val (Int
(TF
));
136 procedure Reset
(Gen
: Generator
; Initiator
: Integer) is
137 Genp
: constant Pointer
:= Gen
.Gen_State
'Unrestricted_Access;
141 X1
:= 2 + Int
(Initiator
) mod (K1
- 3);
142 X2
:= 2 + Int
(Initiator
) mod (K2
- 3);
145 X1
:= Square_Mod_N
(X1
, K1
);
146 X2
:= Square_Mod_N
(X2
, K2
);
149 -- eliminate effects of small Initiators.
164 procedure Reset
(Gen
: Generator
) is
165 Genp
: constant Pointer
:= Gen
.Gen_State
'Unrestricted_Access;
166 Now
: constant Calendar
.Time
:= Calendar
.Clock
;
171 X1
:= Int
(Calendar
.Year
(Now
)) * 12 * 31 +
172 Int
(Calendar
.Month
(Now
) * 31) +
173 Int
(Calendar
.Day
(Now
));
175 X2
:= Int
(Calendar
.Seconds
(Now
) * Duration (1000.0));
177 X1
:= 2 + X1
mod (K1
- 3);
178 X2
:= 2 + X2
mod (K2
- 3);
180 -- Eliminate visible effects of same day starts
183 X1
:= Square_Mod_N
(X1
, K1
);
184 X2
:= Square_Mod_N
(X2
, K2
);
201 procedure Reset
(Gen
: Generator
; From_State
: State
) is
202 Genp
: constant Pointer
:= Gen
.Gen_State
'Unrestricted_Access;
205 Genp
.all := From_State
;
212 procedure Save
(Gen
: Generator
; To_State
: out State
) is
214 To_State
:= Gen
.Gen_State
;
221 function Square_Mod_N
(X
, N
: Int
) return Int
is
223 return Int
((Integer_64
(X
) ** 2) mod (Integer_64
(N
)));
230 function Value
(Coded_State
: String) return State
is
231 Start
: Positive := Coded_State
'First;
232 Stop
: Positive := Coded_State
'First;
236 while Coded_State
(Stop
) /= ',' loop
240 Outs
.X1
:= Int
'Value (Coded_State
(Start
.. Stop
- 1));
245 exit when Coded_State
(Stop
) = ',';
248 Outs
.X2
:= Int
'Value (Coded_State
(Start
.. Stop
- 1));
249 Outs
.Q
:= Int
'Value (Coded_State
(Stop
+ 1 .. Coded_State
'Last));
250 Outs
.P
:= Outs
.Q
* 2 + 1;
251 Outs
.FP
:= Flt
(Outs
.P
);
252 Outs
.Scl
:= (RstL
- RstF
+ 1.0) / (Flt
(Outs
.P
) * Flt
(Outs
.Q
));
254 -- Now do *some* sanity checks.
257 or else Outs
.X1
not in 2 .. Outs
.P
- 1
258 or else Outs
.X2
not in 2 .. Outs
.Q
- 1
260 raise Constraint_Error
;
266 end Ada
.Numerics
.Discrete_Random
;