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1 // Copyright 2016 The Chromium Authors. All rights reserved. | 1 // Copyright 2016 The Chromium Authors. All rights reserved. |
2 // Use of this source code is governed by a BSD-style license that can be | 2 // Use of this source code is governed by a BSD-style license that can be |
3 // found in the LICENSE file. | 3 // found in the LICENSE file. |
4 | 4 |
5 #ifndef BASE_BIT_CAST_H_ | 5 #ifndef BASE_BIT_CAST_H_ |
6 #define BASE_BIT_CAST_H_ | 6 #define BASE_BIT_CAST_H_ |
7 | 7 |
8 #include <string.h> | 8 #include <string.h> |
9 #include <type_traits> | 9 #include <type_traits> |
10 | 10 |
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57 // Fortunately memcpy() is very fast. In optimized mode, compilers replace | 57 // Fortunately memcpy() is very fast. In optimized mode, compilers replace |
58 // calls to memcpy() with inline object code when the size argument is a | 58 // calls to memcpy() with inline object code when the size argument is a |
59 // compile-time constant. On a 32-bit system, memcpy(d,s,4) compiles to one | 59 // compile-time constant. On a 32-bit system, memcpy(d,s,4) compiles to one |
60 // load and one store, and memcpy(d,s,8) compiles to two loads and two stores. | 60 // load and one store, and memcpy(d,s,8) compiles to two loads and two stores. |
61 | 61 |
62 template <class Dest, class Source> | 62 template <class Dest, class Source> |
63 inline Dest bit_cast(const Source& source) { | 63 inline Dest bit_cast(const Source& source) { |
64 static_assert(sizeof(Dest) == sizeof(Source), | 64 static_assert(sizeof(Dest) == sizeof(Source), |
65 "bit_cast requires source and destination to be the same size"); | 65 "bit_cast requires source and destination to be the same size"); |
66 | 66 |
67 #if ((defined(__GLIBCXX__) && (__GLIBCXX__ >= 20150422)) || \ | 67 #if (__GNUC__ > 5 || (__GNUC__ == 5 && __GNUC_MINOR__ >= 1)) |
Nico
2016/04/06 00:39:40
this drops the _libcpp_version check; that's proba
Mostyn Bramley-Moore
2016/04/06 07:54:23
Right- added this back.
| |
68 defined(_LIBCPP_VERSION)) | |
69 // GCC 5.1 contains the first libstdc++ with is_trivially_copyable. | 68 // GCC 5.1 contains the first libstdc++ with is_trivially_copyable. |
70 // Assume libc++ Just Works: is_trivially_copyable added on May 13th 2011. | 69 // Assume libc++ Just Works: is_trivially_copyable added on May 13th 2011. |
71 static_assert(std::is_trivially_copyable<Dest>::value, | 70 static_assert(std::is_trivially_copyable<Dest>::value, |
72 "non-trivially-copyable bit_cast is undefined"); | 71 "non-trivially-copyable bit_cast is undefined"); |
73 static_assert(std::is_trivially_copyable<Source>::value, | 72 static_assert(std::is_trivially_copyable<Source>::value, |
74 "non-trivially-copyable bit_cast is undefined"); | 73 "non-trivially-copyable bit_cast is undefined"); |
75 #elif __has_feature(is_trivially_copyable) | 74 #elif __has_feature(is_trivially_copyable) |
76 // The compiler supports an equivalent intrinsic. | 75 // The compiler supports an equivalent intrinsic. |
77 static_assert(__is_trivially_copyable(Dest), | 76 static_assert(__is_trivially_copyable(Dest), |
78 "non-trivially-copyable bit_cast is undefined"); | 77 "non-trivially-copyable bit_cast is undefined"); |
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89 #else | 88 #else |
90 // Do nothing, let the bots handle it. | 89 // Do nothing, let the bots handle it. |
91 #endif | 90 #endif |
92 | 91 |
93 Dest dest; | 92 Dest dest; |
94 memcpy(&dest, &source, sizeof(dest)); | 93 memcpy(&dest, &source, sizeof(dest)); |
95 return dest; | 94 return dest; |
96 } | 95 } |
97 | 96 |
98 #endif // BASE_BIT_CAST_H_ | 97 #endif // BASE_BIT_CAST_H_ |
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