1 /*
2 * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #ifndef SHARE_VM_METAPROGRAMMING_INTEGERTYPES_HPP
26 #define SHARE_VM_METAPROGRAMMING_INTEGERTYPES_HPP
27
28 #include "memory/allocation.hpp"
29 #include "metaprogramming/enableIf.hpp"
30 #include "metaprogramming/integralConstant.hpp"
31 #include "metaprogramming/isFloatingPoint.hpp"
32 #include "metaprogramming/isIntegral.hpp"
33 #include "metaprogramming/isRegisteredEnum.hpp"
34 #include "utilities/debug.hpp"
35
36 class IntegerTypes : public AllStatic {
37 public:
38 // Return a value of type T with the same representation as x.
39 //
40 // T and U must be of the same size.
41 //
42 // At least one of T or U must be an integral type. The other must
43 // be an integral, floating point, or pointer type.
44 template<typename T, typename U> static T cast(U x);
45
46 // Support thin wrappers over primitive types.
47 // If derived from TrueType, provides representational conversion
48 // from T to some other type. When true, must provide
49 // - Value: typedef for T.
50 // - Decayed: typedef for decayed type.
51 // - static Decayed decay(T x): return value of type Decayed with
52 // the same representation as x.
53 // - static T recover(Decayed x): return a value of type T with the
54 // same representation as x.
55 template<typename T> struct Translate : public FalseType {};
56
57 private:
58
59 template<typename T,
60 typename U,
61 bool same_size = sizeof(T) == sizeof(U),
62 typename Enable = void>
63 struct Cast;
64
65 template<typename T, typename U> static T cast_using_union(U x);
66 };
67
68 // Return an object of type T with the same value representation as x.
69 //
70 // T and U must be of the same size. It is expected that one of T and
71 // U is an integral type, and the other is an integral type, a
72 // (registered) enum type, or a floating point type
73 //
74 // This implementation uses the "union trick", which seems to be the
75 // best of a bad set of options. Though technically undefined
76 // behavior, it is widely and well supported, producing good code. In
77 // some cases, such as gcc, that support is explicitly documented.
78 //
79 // Using memcpy is the correct method, but some compilers produce
80 // wretched code for that method, even at maximal optimization levels.
81 //
82 // Using static_cast is only possible for integral and enum types, not
83 // for floating point types. And for integral and enum conversions,
84 // static_cast has unspecified or implementation-defined behavior for
85 // some cases. C++11 <type_traits> can be used to avoid most or all
86 // of those unspecified or implementation-defined issues, though that
87 // may require multi-step conversions.
88 //
89 // Using reinterpret_cast of references has undefined behavior for
90 // many cases, and there is much less empirical basis for its use, as
91 // compared to the union trick.
92 template<typename T, typename U>
93 inline T IntegerTypes::cast_using_union(U x) {
94 STATIC_ASSERT(sizeof(T) == sizeof(U));
95 union { T t; U u; };
96 u = x;
97 return t;
98 }
99
100 //////////////////////////////////////////////////////////////////////////////
101 // cast<T>(x)
102 //
103 // Cast<T, U, same_size, Enable>
104
105 // Give an informative error if the sizes differ.
106 template<typename T, typename U>
107 struct IntegerTypes::Cast<T, U, false> VALUE_OBJ_CLASS_SPEC {
108 STATIC_ASSERT(sizeof(T) == sizeof(U));
109 };
110
111 // Conversion between integral types.
112 template<typename T, typename U>
113 struct IntegerTypes::Cast<
114 T, U, true,
115 typename EnableIf<IsIntegral<T>::value && IsIntegral<U>::value>::type>
116 VALUE_OBJ_CLASS_SPEC
117 {
118 T operator()(U x) const { return cast_using_union<T>(x); }
119 };
120
121 // Convert an enum or floating point value to an integer value.
122 template<typename T, typename U>
123 struct IntegerTypes::Cast<
124 T, U, true,
125 typename EnableIf<IsIntegral<T>::value &&
126 (IsRegisteredEnum<U>::value ||
127 IsFloatingPoint<U>::value)>::type>
128 VALUE_OBJ_CLASS_SPEC
129 {
130 T operator()(U x) const { return cast_using_union<T>(x); }
131 };
132
133 // Convert an integer to an enum or floating point value.
134 template<typename T, typename U>
135 struct IntegerTypes::Cast<
136 T, U, true,
137 typename EnableIf<IsIntegral<U>::value &&
138 (IsRegisteredEnum<T>::value ||
139 IsFloatingPoint<T>::value)>::type>
140 VALUE_OBJ_CLASS_SPEC
141 {
142 T operator()(U x) const { return cast_using_union<T>(x); }
143 };
144
145 // Convert a pointer to an integral value.
146 template<typename T, typename U>
147 struct IntegerTypes::Cast<
148 T, U*, true,
149 typename EnableIf<IsIntegral<T>::value>::type>
150 VALUE_OBJ_CLASS_SPEC
151 {
152 T operator()(U* x) const { return reinterpret_cast<T>(x); }
153 };
154
155 // Convert an integral value to a pointer.
156 template<typename T, typename U>
157 struct IntegerTypes::Cast<
158 T*, U, true,
159 typename EnableIf<IsIntegral<U>::value>::type>
160 VALUE_OBJ_CLASS_SPEC
161 {
162 T* operator()(U x) const { return reinterpret_cast<T*>(x); }
163 };
164
165 template<typename T, typename U>
166 inline T IntegerTypes::cast(U x) {
167 return Cast<T, U>()(x);
168 }
169
170 #endif // SHARE_VM_METAPROGRAMMING_INTEGERTYPES_HPP