1 ------------------------------------------------------------------------------
3 -- GNAT RUNTIME COMPONENTS --
5 -- S Y S T E M . E X N _ G E N --
10 -- Copyright (C) 1992-2001, 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 -- Extensive contributions were provided by Ada Core Technologies Inc. --
33 ------------------------------------------------------------------------------
35 package body System
.Exn_Gen
is
41 function Exn_Float_Type
46 pragma Suppress
(Division_Check
);
47 pragma Suppress
(Overflow_Check
);
48 pragma Suppress
(Range_Check
);
50 Result
: Type_Of_Base
:= 1.0;
51 Factor
: Type_Of_Base
:= Left
;
52 Exp
: Integer := Right
;
55 -- We use the standard logarithmic approach, Exp gets shifted right
56 -- testing successive low order bits and Factor is the value of the
57 -- base raised to the next power of 2. For positive exponents we
58 -- multiply the result by this factor, for negative exponents, we
59 -- Division by this factor.
63 if Exp
rem 2 /= 0 then
64 Result
:= Result
* Factor
;
69 Factor
:= Factor
* Factor
;
74 -- Negative exponent. For a zero base, we should arguably return an
75 -- infinity of the right sign, but it is not clear that there is
76 -- proper authorization to do so, so for now raise Constraint_Error???
78 elsif Factor
= 0.0 then
79 raise Constraint_Error
;
81 -- Here we have a non-zero base and a negative exponent
84 -- For the negative exponent case, a constraint error during this
85 -- calculation happens if Factor gets too large, and the proper
86 -- response is to return 0.0, since what we essentially have is
87 -- 1.0 / infinity, and the closest model number will be zero.
91 if Exp
rem 2 /= 0 then
92 Result
:= Result
* Factor
;
97 Factor
:= Factor
* Factor
;
104 when Constraint_Error
=>
110 ----------------------
111 -- Exn_Integer_Type --
112 ----------------------
114 -- Note that negative exponents get a constraint error because the
115 -- subtype of the Right argument (the exponent) is Natural.
117 function Exn_Integer_Type
118 (Left
: Type_Of_Base
;
122 pragma Suppress
(Division_Check
);
123 pragma Suppress
(Overflow_Check
);
125 Result
: Type_Of_Base
:= 1;
126 Factor
: Type_Of_Base
:= Left
;
127 Exp
: Natural := Right
;
130 -- We use the standard logarithmic approach, Exp gets shifted right
131 -- testing successive low order bits and Factor is the value of the
132 -- base raised to the next power of 2.
134 -- Note: it is not worth special casing the cases of base values -1,0,+1
135 -- since the expander does this when the base is a literal, and other
136 -- cases will be extremely rare.
140 if Exp
rem 2 /= 0 then
141 Result
:= Result
* Factor
;
146 Factor
:= Factor
* Factor
;
151 end Exn_Integer_Type
;