1 ------------------------------------------------------------------------------
3 -- GNAT RUNTIME COMPONENTS --
5 -- S Y S T E M . E X N _ G E N --
9 -- Copyright (C) 1992-2001, Free Software Foundation, Inc. --
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 2, 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. See the GNU General Public License --
17 -- for more details. You should have received a copy of the GNU General --
18 -- Public License distributed with GNAT; see file COPYING. If not, write --
19 -- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
20 -- MA 02111-1307, USA. --
22 -- As a special exception, if other files instantiate generics from this --
23 -- unit, or you link this unit with other files to produce an executable, --
24 -- this unit does not by itself cause the resulting executable to be --
25 -- covered by the GNU General Public License. This exception does not --
26 -- however invalidate any other reasons why the executable file might be --
27 -- covered by the GNU Public License. --
29 -- GNAT was originally developed by the GNAT team at New York University. --
30 -- Extensive contributions were provided by Ada Core Technologies Inc. --
32 ------------------------------------------------------------------------------
34 package body System
.Exn_Gen
is
40 function Exn_Float_Type
45 pragma Suppress
(Division_Check
);
46 pragma Suppress
(Overflow_Check
);
47 pragma Suppress
(Range_Check
);
49 Result
: Type_Of_Base
:= 1.0;
50 Factor
: Type_Of_Base
:= Left
;
51 Exp
: Integer := Right
;
54 -- We use the standard logarithmic approach, Exp gets shifted right
55 -- testing successive low order bits and Factor is the value of the
56 -- base raised to the next power of 2. For positive exponents we
57 -- multiply the result by this factor, for negative exponents, we
58 -- Division by this factor.
62 if Exp
rem 2 /= 0 then
63 Result
:= Result
* Factor
;
68 Factor
:= Factor
* Factor
;
73 -- Negative exponent. For a zero base, we should arguably return an
74 -- infinity of the right sign, but it is not clear that there is
75 -- proper authorization to do so, so for now raise Constraint_Error???
77 elsif Factor
= 0.0 then
78 raise Constraint_Error
;
80 -- Here we have a non-zero base and a negative exponent
83 -- For the negative exponent case, a constraint error during this
84 -- calculation happens if Factor gets too large, and the proper
85 -- response is to return 0.0, since what we essentially have is
86 -- 1.0 / infinity, and the closest model number will be zero.
90 if Exp
rem 2 /= 0 then
91 Result
:= Result
* Factor
;
96 Factor
:= Factor
* Factor
;
103 when Constraint_Error
=>
109 ----------------------
110 -- Exn_Integer_Type --
111 ----------------------
113 -- Note that negative exponents get a constraint error because the
114 -- subtype of the Right argument (the exponent) is Natural.
116 function Exn_Integer_Type
117 (Left
: Type_Of_Base
;
121 pragma Suppress
(Division_Check
);
122 pragma Suppress
(Overflow_Check
);
124 Result
: Type_Of_Base
:= 1;
125 Factor
: Type_Of_Base
:= Left
;
126 Exp
: Natural := Right
;
129 -- We use the standard logarithmic approach, Exp gets shifted right
130 -- testing successive low order bits and Factor is the value of the
131 -- base raised to the next power of 2.
133 -- Note: it is not worth special casing the cases of base values -1,0,+1
134 -- since the expander does this when the base is a literal, and other
135 -- cases will be extremely rare.
139 if Exp
rem 2 /= 0 then
140 Result
:= Result
* Factor
;
145 Factor
:= Factor
* Factor
;
150 end Exn_Integer_Type
;