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enum-flags.h
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1 /* Copyright (C) 2015-2018 Free Software Foundation, Inc.
2
3 This file is part of GDB.
4
5 This program is free software; you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 3 of the License, or
8 (at your option) any later version.
9
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
14
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>. */
17
18 #ifndef COMMON_ENUM_FLAGS_H
19 #define COMMON_ENUM_FLAGS_H
20
21 /* Type-safe wrapper for enum flags. enum flags are enums where the
22 values are bits that are meant to be ORed together.
23
24 This allows writing code like the below, while with raw enums this
25 would fail to compile without casts to enum type at the assignments
26 to 'f':
27
28 enum some_flag
29 {
30 flag_val1 = 1 << 1,
31 flag_val2 = 1 << 2,
32 flag_val3 = 1 << 3,
33 flag_val4 = 1 << 4,
34 };
35 DEF_ENUM_FLAGS_TYPE(enum some_flag, some_flags)
36
37 some_flags f = flag_val1 | flag_val2;
38 f |= flag_val3;
39
40 It's also possible to assign literal zero to an enum flags variable
41 (meaning, no flags), dispensing adding an awkward explicit "no
42 value" value to the enumeration. For example:
43
44 some_flags f = 0;
45 f |= flag_val3 | flag_val4;
46
47 Note that literal integers other than zero fail to compile:
48
49 some_flags f = 1; // error
50 */
51
52 #ifdef __cplusplus
53
54 /* Traits type used to prevent the global operator overloads from
55 instantiating for non-flag enums. */
56 template<typename T> struct enum_flags_type {};
57
58 /* Use this to mark an enum as flags enum. It defines FLAGS as
59 enum_flags wrapper class for ENUM, and enables the global operator
60 overloads for ENUM. */
61 #define DEF_ENUM_FLAGS_TYPE(enum_type, flags_type) \
62 typedef enum_flags<enum_type> flags_type; \
63 template<> \
64 struct enum_flags_type<enum_type> \
65 { \
66 typedef enum_flags<enum_type> type; \
67 }
68
69 /* Until we can rely on std::underlying type being universally
70 available (C++11), roll our own for enums. */
71 template<int size, bool sign> class integer_for_size { typedef void type; };
72 template<> struct integer_for_size<1, 0> { typedef uint8_t type; };
73 template<> struct integer_for_size<2, 0> { typedef uint16_t type; };
74 template<> struct integer_for_size<4, 0> { typedef uint32_t type; };
75 template<> struct integer_for_size<8, 0> { typedef uint64_t type; };
76 template<> struct integer_for_size<1, 1> { typedef int8_t type; };
77 template<> struct integer_for_size<2, 1> { typedef int16_t type; };
78 template<> struct integer_for_size<4, 1> { typedef int32_t type; };
79 template<> struct integer_for_size<8, 1> { typedef int64_t type; };
80
81 template<typename T>
82 struct enum_underlying_type
83 {
84 typedef typename
85 integer_for_size<sizeof (T), static_cast<bool>(T (-1) < T (0))>::type
86 type;
87 };
88
89 template <typename E>
90 class enum_flags
91 {
92 public:
93 typedef E enum_type;
94 typedef typename enum_underlying_type<enum_type>::type underlying_type;
95
96 private:
97 /* Private type used to support initializing flag types with zero:
98
99 foo_flags f = 0;
100
101 but not other integers:
102
103 foo_flags f = 1;
104
105 The way this works is that we define an implicit constructor that
106 takes a pointer to this private type. Since nothing can
107 instantiate an object of this type, the only possible pointer to
108 pass to the constructor is the NULL pointer, or, zero. */
109 struct zero_type;
110
111 underlying_type
112 underlying_value () const
113 {
114 return m_enum_value;
115 }
116
117 public:
118 /* Allow default construction. */
119 enum_flags ()
120 : m_enum_value ((enum_type) 0)
121 {}
122
123 /* If you get an error saying these two overloads are ambiguous,
124 then you tried to mix values of different enum types. */
125 enum_flags (enum_type e)
126 : m_enum_value (e)
127 {}
128 enum_flags (struct enum_flags::zero_type *zero)
129 : m_enum_value ((enum_type) 0)
130 {}
131
132 enum_flags &operator&= (enum_type e)
133 {
134 m_enum_value = (enum_type) (underlying_value () & e);
135 return *this;
136 }
137 enum_flags &operator|= (enum_type e)
138 {
139 m_enum_value = (enum_type) (underlying_value () | e);
140 return *this;
141 }
142 enum_flags &operator^= (enum_type e)
143 {
144 m_enum_value = (enum_type) (underlying_value () ^ e);
145 return *this;
146 }
147
148 operator enum_type () const
149 {
150 return m_enum_value;
151 }
152
153 enum_flags operator& (enum_type e) const
154 {
155 return (enum_type) (underlying_value () & e);
156 }
157 enum_flags operator| (enum_type e) const
158 {
159 return (enum_type) (underlying_value () | e);
160 }
161 enum_flags operator^ (enum_type e) const
162 {
163 return (enum_type) (underlying_value () ^ e);
164 }
165 enum_flags operator~ () const
166 {
167 return (enum_type) ~underlying_value ();
168 }
169
170 private:
171 /* Stored as enum_type because GDB knows to print the bit flags
172 neatly if the enum values look like bit flags. */
173 enum_type m_enum_value;
174 };
175
176 /* Global operator overloads. */
177
178 template <typename enum_type>
179 typename enum_flags_type<enum_type>::type
180 operator& (enum_type e1, enum_type e2)
181 {
182 return enum_flags<enum_type> (e1) & e2;
183 }
184
185 template <typename enum_type>
186 typename enum_flags_type<enum_type>::type
187 operator| (enum_type e1, enum_type e2)
188 {
189 return enum_flags<enum_type> (e1) | e2;
190 }
191
192 template <typename enum_type>
193 typename enum_flags_type<enum_type>::type
194 operator^ (enum_type e1, enum_type e2)
195 {
196 return enum_flags<enum_type> (e1) ^ e2;
197 }
198
199 template <typename enum_type>
200 typename enum_flags_type<enum_type>::type
201 operator~ (enum_type e)
202 {
203 return ~enum_flags<enum_type> (e);
204 }
205
206 #else /* __cplusplus */
207
208 /* In C, the flags type is just a typedef for the enum type. */
209
210 #define DEF_ENUM_FLAGS_TYPE(enum_type, flags_type) \
211 typedef enum_type flags_type
212
213 #endif /* __cplusplus */
214
215 #endif /* COMMON_ENUM_FLAGS_H */