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// SPDX-FileCopyrightText: Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
// SPDX-License-Identifier: BSD-3-Clause
/**
* @class vtkHashCombiner
* @brief Combine 4- and 8-byte integers into a single hash value.
*
* This templated class accepts one 4- or 8-byte integer
* and combines it with an existing hash. It is useful for
* combining hashes of strings with integer values such as
* connectivity entries for shape primitives.
*
* This class was adapted from (i.e., uses the integer constants from)
* boost::hash_combine but adds the templating on input value sizes.
*
* \sa vtkCellGridSidesQuery for an example of its use.
*/
#ifndef vtkHashCombiner_h
#define vtkHashCombiner_h
#include "vtkCommonCoreModule.h" // For export macro
#include <cstdint> // For uint32_t.
VTK_ABI_NAMESPACE_BEGIN
class VTKCOMMONCORE_EXPORT VTK_WRAPEXCLUDE vtkHashCombiner
{
public:
/// Combine an integer \a k with the 64-bit hash \a h (which is modified on exit).
template <typename T>
void operator()(T& h, typename std::enable_if<sizeof(T) == 8, std::size_t>::type k)
{
constexpr T m = 0xc6a4a7935bd1e995ull;
constexpr int r = 47;
k *= m;
k ^= k >> r;
k *= m;
h ^= k;
h *= m;
// Completely arbitrary number, to prevent 0's
// from hashing to 0.
h += 0xe6546b64;
}
/// Combine an integer \a k with the 32-bit hash \a h (which is modified on exit).
template <typename T>
void operator()(T& h, typename std::enable_if<sizeof(T) == 4, std::size_t>::type k)
{
constexpr std::uint32_t c1 = 0xcc9e2d51;
constexpr std::uint32_t c2 = 0x1b873593;
constexpr std::uint32_t r1 = 15;
constexpr std::uint32_t r2 = 13;
k *= c1;
k = (k << r1) | (k >> (32 - r1));
k *= c2;
h ^= k;
h = (h << r2) | (h >> (32 - r2));
h = h * 5 + 0xe6546b64;
}
};
VTK_ABI_NAMESPACE_END
#endif // vtkHashCombiner_h
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