mirror of
https://gitlab.kitware.com/vtk/vtk-m
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96 lines
3.9 KiB
C++
96 lines
3.9 KiB
C++
//============================================================================
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// Copyright (c) Kitware, Inc.
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// All rights reserved.
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// See LICENSE.txt for details.
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//
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// This software is distributed WITHOUT ANY WARRANTY; without even
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// the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
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// PURPOSE. See the above copyright notice for more information.
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//============================================================================
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#ifndef vtk_m_count_ArrayHandleRandomUniformReal_h
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#define vtk_m_count_ArrayHandleRandomUniformReal_h
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#include <vtkm/cont/ArrayHandleRandomUniformBits.h>
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#include <vtkm/cont/ArrayHandleTransform.h>
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namespace vtkm
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{
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namespace cont
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{
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namespace detail
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{
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template <typename Real>
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struct CanonicalFunctor;
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template <>
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struct CanonicalFunctor<vtkm::Float64>
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{
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/// \brief VTKm's equivalent of std::generate_canonical, turning a random bit source into
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/// random real number in the range of [0, 1).
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// We take 53 bits (number of bits in mantissa in a double) from the 64 bits random source
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// and divide it by (1 << 53).
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static constexpr vtkm::Float64 DIVISOR = static_cast<vtkm::Float64>(vtkm::UInt64{ 1 } << 53);
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static constexpr vtkm::UInt64 MASK = (vtkm::UInt64{ 1 } << 53) - vtkm::UInt64{ 1 };
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VTKM_EXEC_CONT
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vtkm::Float64 operator()(vtkm::UInt64 bits) const { return (bits & MASK) / DIVISOR; }
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};
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template <>
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struct CanonicalFunctor<vtkm::Float32>
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{
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// We take 24 bits (number of bits in mantissa in a double) from the 64 bits random source
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// and divide it by (1 << 24).
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static constexpr vtkm::Float32 DIVISOR = static_cast<vtkm::Float32>(vtkm::UInt32{ 1 } << 24);
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static constexpr vtkm::UInt32 MASK = (vtkm::UInt32{ 1 } << 24) - vtkm::UInt32{ 1 };
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VTKM_EXEC_CONT
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vtkm::Float32 operator()(vtkm::UInt64 bits) const { return (bits & MASK) / DIVISOR; }
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};
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} // detail
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/// @brief An `ArrayHandle` that provides a source of random numbers with uniform distribution.
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///
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/// `ArrayHandleRandomUniformReal` takes a user supplied seed and hashes it to provide
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/// a sequence of numbers drawn from a random uniform distribution in the range [0, 1).
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/// `ArrayHandleRandomUniformReal` is built on top of `ArrayHandleRandomUniformBits` so
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/// shares its behavior with that array.
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///
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/// Note: In contrast to traditional random number generator,
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/// `ArrayHandleRandomUniformReal` does not have "state", i.e. multiple calls
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/// the Get() method with the same index will always return the same hash value.
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/// To get a new set of random bits, create a new `ArrayHandleRandomUniformBits`
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/// with a different seed.
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template <typename Real = vtkm::Float64>
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class VTKM_ALWAYS_EXPORT ArrayHandleRandomUniformReal
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: public vtkm::cont::ArrayHandleTransform<vtkm::cont::ArrayHandleRandomUniformBits,
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detail::CanonicalFunctor<Real>>
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{
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public:
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using SeedType = vtkm::Vec<vtkm::UInt32, 1>;
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VTKM_ARRAY_HANDLE_SUBCLASS(
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ArrayHandleRandomUniformReal,
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(ArrayHandleRandomUniformReal<Real>),
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(vtkm::cont::ArrayHandleTransform<vtkm::cont::ArrayHandleRandomUniformBits,
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detail::CanonicalFunctor<Real>>));
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/// Construct an `ArrayHandleRandomUniformReal`.
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///
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/// @param length Specifies the length of the generated array.
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/// @param seed Provides a seed to use for the pseudorandom numbers. To prevent confusion
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/// between the seed and the length, the type of the seed is a `vtkm::Vec` of size 1. To
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/// specify the seed, declare it in braces. For example, to construct a random array of
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/// size 50 with seed 123, use `ArrayHandleRandomUniformReal(50, { 123 })`.
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explicit ArrayHandleRandomUniformReal(vtkm::Id length, SeedType seed = { std::random_device{}() })
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: Superclass(vtkm::cont::ArrayHandleRandomUniformBits{ length, seed },
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detail::CanonicalFunctor<Real>{})
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{
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}
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};
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} // cont
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} // vtkm
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#endif //vtk_m_count_ArrayHandleRandomUniformReal_h
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