53 lines
1.9 KiB
C
53 lines
1.9 KiB
C
// Copyright 2016 Google LLC. All rights reserved.
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//
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file or at
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// https://developers.google.com/open-source/licenses/bsd
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#ifndef PACKAGER_MEDIA_BASE_MACROS_H_
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#define PACKAGER_MEDIA_BASE_MACROS_H_
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// The FALLTHROUGH_INTENDED macro can be used to annotate implicit fall-through
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// between switch labels:
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// switch (x) {
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// case 40:
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// case 41:
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// if (truth_is_out_there) {
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// ++x;
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// FALLTHROUGH_INTENDED; // Use instead of/along with annotations in
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// // comments.
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// } else {
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// return x;
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// }
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// case 42:
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// ...
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//
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// As shown in the example above, the FALLTHROUGH_INTENDED macro should be
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// followed by a semicolon. It is designed to mimic control-flow statements
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// like 'break;', so it can be placed in most places where 'break;' can, but
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// only if there are no statements on the execution path between it and the
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// next switch label.
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//
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// When compiled with clang in C++11 mode, the FALLTHROUGH_INTENDED macro is
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// expanded to [[clang::fallthrough]] attribute, which is analysed when
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// performing switch labels fall-through diagnostic ('-Wimplicit-fallthrough').
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// See clang documentation on language extensions for details:
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// http://clang.llvm.org/docs/AttributeReference.html#fallthrough-clang-fallthrough
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//
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// When used with unsupported compilers, the FALLTHROUGH_INTENDED macro has no
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// effect on diagnostics.
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//
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// In either case this macro has no effect on runtime behavior and performance
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// of code.
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#if defined(__clang__) && __cplusplus >= 201103L && defined(__has_warning)
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#if __has_feature(cxx_attributes) && __has_warning("-Wimplicit-fallthrough")
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#define FALLTHROUGH_INTENDED [[clang::fallthrough]] // NOLINT
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#endif
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#endif
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#ifndef FALLTHROUGH_INTENDED
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#define FALLTHROUGH_INTENDED [[fallthrough]]
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#endif
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#endif // PACKAGER_MEDIA_BASE_MACROS_H_
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