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1 | ------------------------------------------------------------------------------ |
2 | -- -- | |
3 | -- GNAT RUNTIME COMPONENTS -- | |
4 | -- -- | |
5 | -- S Y S T E M . E X P _ G E N -- | |
6 | -- -- | |
7 | -- B o d y -- | |
8 | -- -- | |
cacbc350 RK |
9 | -- Copyright (C) 1992-2001, Free Software Foundation, Inc. -- |
10 | -- -- | |
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. -- | |
21 | -- -- | |
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. -- | |
28 | -- -- | |
29 | -- GNAT was originally developed by the GNAT team at New York University. -- | |
71ff80dc | 30 | -- Extensive contributions were provided by Ada Core Technologies Inc. -- |
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31 | -- -- |
32 | ------------------------------------------------------------------------------ | |
33 | ||
34 | package body System.Exp_Gen is | |
35 | ||
36 | -------------------- | |
37 | -- Exp_Float_Type -- | |
38 | -------------------- | |
39 | ||
40 | function Exp_Float_Type | |
41 | (Left : Type_Of_Base; | |
42 | Right : Integer) | |
43 | return Type_Of_Base | |
44 | is | |
45 | Result : Type_Of_Base := 1.0; | |
46 | Factor : Type_Of_Base := Left; | |
47 | Exp : Integer := Right; | |
48 | ||
49 | begin | |
50 | -- We use the standard logarithmic approach, Exp gets shifted right | |
51 | -- testing successive low order bits and Factor is the value of the | |
52 | -- base raised to the next power of 2. For positive exponents we | |
53 | -- multiply the result by this factor, for negative exponents, we | |
54 | -- divide by this factor. | |
55 | ||
56 | if Exp >= 0 then | |
57 | ||
58 | -- For a positive exponent, if we get a constraint error during | |
59 | -- this loop, it is an overflow, and the constraint error will | |
60 | -- simply be passed on to the caller. | |
61 | ||
62 | loop | |
63 | if Exp rem 2 /= 0 then | |
64 | declare | |
65 | pragma Unsuppress (All_Checks); | |
66 | begin | |
67 | Result := Result * Factor; | |
68 | end; | |
69 | end if; | |
70 | ||
71 | Exp := Exp / 2; | |
72 | exit when Exp = 0; | |
73 | ||
74 | declare | |
75 | pragma Unsuppress (All_Checks); | |
76 | begin | |
77 | Factor := Factor * Factor; | |
78 | end; | |
79 | end loop; | |
80 | ||
81 | return Result; | |
82 | ||
83 | -- Now we know that the exponent is negative, check for case of | |
84 | -- base of 0.0 which always generates a constraint error. | |
85 | ||
86 | elsif Factor = 0.0 then | |
87 | raise Constraint_Error; | |
88 | ||
89 | -- Here we have a negative exponent with a non-zero base | |
90 | ||
91 | else | |
92 | ||
93 | -- For the negative exponent case, a constraint error during this | |
94 | -- calculation happens if Factor gets too large, and the proper | |
95 | -- response is to return 0.0, since what we essenmtially have is | |
96 | -- 1.0 / infinity, and the closest model number will be zero. | |
97 | ||
98 | begin | |
99 | loop | |
100 | if Exp rem 2 /= 0 then | |
101 | declare | |
102 | pragma Unsuppress (All_Checks); | |
103 | begin | |
104 | Result := Result * Factor; | |
105 | end; | |
106 | end if; | |
107 | ||
108 | Exp := Exp / 2; | |
109 | exit when Exp = 0; | |
110 | ||
111 | declare | |
112 | pragma Unsuppress (All_Checks); | |
113 | begin | |
114 | Factor := Factor * Factor; | |
115 | end; | |
116 | end loop; | |
117 | ||
118 | declare | |
119 | pragma Unsuppress (All_Checks); | |
120 | begin | |
121 | return 1.0 / Result; | |
122 | end; | |
123 | ||
124 | exception | |
125 | ||
126 | when Constraint_Error => | |
127 | return 0.0; | |
128 | end; | |
129 | end if; | |
130 | end Exp_Float_Type; | |
131 | ||
132 | ---------------------- | |
133 | -- Exp_Integer_Type -- | |
134 | ---------------------- | |
135 | ||
136 | -- Note that negative exponents get a constraint error because the | |
137 | -- subtype of the Right argument (the exponent) is Natural. | |
138 | ||
139 | function Exp_Integer_Type | |
140 | (Left : Type_Of_Base; | |
141 | Right : Natural) | |
142 | return Type_Of_Base | |
143 | is | |
144 | Result : Type_Of_Base := 1; | |
145 | Factor : Type_Of_Base := Left; | |
146 | Exp : Natural := Right; | |
147 | ||
148 | begin | |
149 | -- We use the standard logarithmic approach, Exp gets shifted right | |
150 | -- testing successive low order bits and Factor is the value of the | |
151 | -- base raised to the next power of 2. | |
152 | ||
153 | -- Note: it is not worth special casing the cases of base values -1,0,+1 | |
154 | -- since the expander does this when the base is a literal, and other | |
155 | -- cases will be extremely rare. | |
156 | ||
157 | if Exp /= 0 then | |
158 | loop | |
159 | if Exp rem 2 /= 0 then | |
160 | declare | |
161 | pragma Unsuppress (All_Checks); | |
162 | begin | |
163 | Result := Result * Factor; | |
164 | end; | |
165 | end if; | |
166 | ||
167 | Exp := Exp / 2; | |
168 | exit when Exp = 0; | |
169 | ||
170 | declare | |
171 | pragma Unsuppress (All_Checks); | |
172 | begin | |
173 | Factor := Factor * Factor; | |
174 | end; | |
175 | end loop; | |
176 | end if; | |
177 | ||
178 | return Result; | |
179 | end Exp_Integer_Type; | |
180 | ||
181 | end System.Exp_Gen; |