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/*=========================================================================
Program: Visualization Toolkit
Module: vtkAssume.h
Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
All rights reserved.
See Copyright.txt or http://www.kitware.com/Copyright.htm for details.
This software is distributed WITHOUT ANY WARRANTY; without even
the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE. See the above copyright notice for more information.
=========================================================================*/
// .NAME VTK_ASSUME - Provide compiler hints for non-obvious conditions.
#ifndef vtkAssume_h
#define vtkAssume_h
#include "vtkConfigure.h"
#include <cassert>
// Description:
// VTK_ASSUME instructs the compiler that a certain non-obvious condition will
// *always* be true. Beware that if cond is false at runtime, the results are
// unpredictable (and likely catastrophic). A runtime assertion is added so
// that debugging builds may easily catch violations of the condition.
//
// A useful application of this macro is when a vtkGenericDataArray subclass has
// a known number of components at compile time. Adding, for example,
// VTK_ASSUME(array->GetNumberOfComponents() == 3); allows the compiler to
// provide faster access through the GetTypedComponent method, as the fixed data
// stride in AOS arrays allows advanced optimization of the accesses.
//
// A more detailed description of this class and related tools can be found
// \ref VTK-7-1-ArrayDispatch "here".
#define VTK_ASSUME(cond) \
do { \
const bool c = cond; \
assert("Bad assumption in VTK_ASSUME: " #cond && c); \
VTK_ASSUME_IMPL(c); \
(void)c; /* Prevents unused var warnings */ \
} while (false) /* do-while prevents extra semicolon warnings */
// VTK_ASSUME_IMPL is compiler-specific:
#if defined(VTK_COMPILER_MSVC) || defined(VTK_COMPILER_ICC)
# define VTK_ASSUME_IMPL(cond) __assume(cond)
#elif defined(VTK_COMPILER_GCC) && VTK_COMPILER_GCC_VERSION >= 40500
// Added in 4.5.0:
# define VTK_ASSUME_IMPL(cond) if (!(cond)) __builtin_unreachable()
#elif defined(VTK_COMPILER_CLANG)
# define VTK_ASSUME_IMPL(cond) if (!(cond)) __builtin_unreachable()
#else
# define VTK_ASSUME_IMPL(cond) do {} while (false) /* no-op */
#endif
#endif // vtkAssume_h
// VTK-HeaderTest-Exclude: vtkAssume.h
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