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 "utilities/debug.hpp"
30 #include "metaprogramming/enableIf.hpp"
31 #include "metaprogramming/integralConstant.hpp"
32 #include "metaprogramming/isFloatingPoint.hpp"
33 #include "metaprogramming/isPointer.hpp"
34 #include "metaprogramming/isRegisteredEnum.hpp"
35 #include "metaprogramming/isIntegral.hpp"
36
37 class IntegerTypes : public AllStatic {
38 public:
39 // Return a value of type T with the same representation as x.
40 //
41 // T and U must be of the same size.
42 //
43 // At least one of T or U must be an integral type. The other must
44 // be an integral, floating point, or pointer type.
45 template<typename T, typename U> static T cast(U x);
46
47 // Support thin wrappers over primitive types.
48 // If derived from TrueType, provides representational conversion
49 // from T to some other type. When true, must provide
50 // - Value: typedef for T.
51 // - Decayed: typedef for decayed type.
52 // - static Decayed decay(T x): return value of type Decayed with
53 // the same representation as x.
54 // - static T recover(Decayed x): return a value of type T with the
55 // same representation as x.
56 template<typename T> struct Translate : public FalseType {};
57
58 // Value categories. For internal use, but needs to be public.
59 enum Category {
60 INTEGRAL,
61 ENUM,
62 FLOAT,
63 POINTER
64 };
65
66 private:
67
68 template<typename T, typename Enable = void> struct GetCategory;
69
70 template<typename T,
71 typename U,
72 bool same_size = sizeof(T) == sizeof(U),
73 Category to_category = GetCategory<T>::value,
74 Category from_category = GetCategory<U>::value>
75 struct Cast;
76
77 template<typename T, typename U> static T cast_integral(U x);
78 template<typename T, typename U> static T cast_floating_point(U x);
79 };
80
81 #define DEFINE_GET_CATEGORY(Predicate, Value) \
82 template<typename T> \
83 struct IntegerTypes::GetCategory< \
84 T, \
85 typename EnableIf<Predicate<T>::value>::type> \
86 : IntegralConstant<IntegerTypes::Category, IntegerTypes::Value> \
87 {};
88
89 DEFINE_GET_CATEGORY(IsIntegral, INTEGRAL)
90 DEFINE_GET_CATEGORY(IsRegisteredEnum, ENUM)
91 DEFINE_GET_CATEGORY(IsFloatingPoint, FLOAT)
92 DEFINE_GET_CATEGORY(IsPointer, POINTER)
93
94 #undef DEFINE_GET_CATEGORY
95
96 // Convert between different integral types of the same size.
97 // See C++03 3.10/15 for discussion of reinterpret_cast to a reference
98 // as a means for converting integral types while keeping the representation.
99 template<typename T, typename U>
100 inline T IntegerTypes::cast_integral(U x) {
101 STATIC_ASSERT(sizeof(T) == sizeof(U));
102 return reinterpret_cast<T&>(x);
103 }
104
105 // Convert between an integral type and a floating point type of the
106 // same size. The only truly correct way to do this is with memcpy.
107 // Both the union trick and type punning via casts are undefined
108 // behavior. gcc generates exactly the same code for all three methods,
109 // except where the UB of type punning causes it to go off into the weeds.
110 // (gcc explicitly supports the union trick.) Other compilers may vary.
111 // In particular, not all compilers do a good job with the memcpy.
112 template<typename T, typename U>
113 inline T IntegerTypes::cast_floating_point(U x) {
114 STATIC_ASSERT(sizeof(T) == sizeof(U));
115 T result;
116 memcpy(&result, &x, sizeof(x));
117 return result;
118 }
119
120 //////////////////////////////////////////////////////////////////////////////
121 // cast<T>(x)
122 //
123 // Cast<T, U, same_size, to_category, from_category>
124
125 // Give an informative error if the sizes differ.
126 template<typename T, typename U,
127 IntegerTypes::Category to_category,
128 IntegerTypes::Category from_category>
129 struct IntegerTypes::Cast<T, U, false, to_category, from_category>
130 VALUE_OBJ_CLASS_SPEC
131 {
132 STATIC_ASSERT(sizeof(T) == sizeof(U));
133 };
134
135 #define DEFINE_INTEGER_TYPES_CAST(To, From, Convert) \
136 template<typename T, typename U> \
137 struct IntegerTypes::Cast<T, U, true, \
138 IntegerTypes::To, \
139 IntegerTypes::From> \
140 VALUE_OBJ_CLASS_SPEC \
141 { \
142 T operator()(U x) const { return Convert<T>(x); } \
143 };
144
145 DEFINE_INTEGER_TYPES_CAST(INTEGRAL, INTEGRAL, cast_integral)
146 DEFINE_INTEGER_TYPES_CAST(ENUM, INTEGRAL, cast_integral)
147 DEFINE_INTEGER_TYPES_CAST(INTEGRAL, ENUM, cast_integral)
148 DEFINE_INTEGER_TYPES_CAST(FLOAT, INTEGRAL, cast_floating_point)
149 DEFINE_INTEGER_TYPES_CAST(INTEGRAL, FLOAT, cast_floating_point)
150 DEFINE_INTEGER_TYPES_CAST(POINTER, INTEGRAL, reinterpret_cast)
151 DEFINE_INTEGER_TYPES_CAST(INTEGRAL, POINTER, reinterpret_cast)
152
153 #undef DEFINE_INTEGER_TYPES_CAST
154
155 template<typename T, typename U>
156 inline T IntegerTypes::cast(U x) {
157 return Cast<T, U>()(x);
158 }
159
160 #endif // SHARE_VM_METAPROGRAMMING_INTEGERTYPES_HPP