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/*=========================================================================
*
* Copyright NumFOCUS
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0.txt
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*=========================================================================*/
#ifndef itkImageHelper_h
#define itkImageHelper_h
#include "itkMacro.h" // For ITK_TEMPLATE_EXPORT.
namespace itk
{
/** \class ImageHelper
* \brief Fast Index/Offset computation
*
* These helper methods use recursive templates to unroll the loops
* of simple calculations. The resulting speed improvement varies from
* compiler to compiler. Some gcc compilers with debug turned on
* exhibit slight speed increases, but most compilers see
* improvement. The ComputeOffset performance improvement is
* impressive. For example, the Windows VS7.0 compiler shows almost a
* factor of 2 speed improvement with the recursive templates. Usually
* recursive templates use partial specialization to terminate
* loops. Here we use a technique used by Brad King in the itk Concept
* Checking code.
*
* \note This work is part of the National Alliance for Medical Image
* Computing (NAMIC), funded by the National Institutes of Health
* through the NIH Roadmap for Medical Research, Grant U54 EB005149.
* Information on the National Centers for Biomedical Computing
* can be obtained from http://commonfund.nih.gov/bioinformatics.
*
* \ingroup ITKCommon
*/
// Forward reference because of circular dependencies
template <unsigned int VImageDimension>
class ITK_TEMPLATE_EXPORT ImageBase;
template <unsigned int VImageDimension, unsigned int VLoop>
class ImageHelper
{
public:
using ImageType = ImageBase<VImageDimension>;
using IndexType = typename ImageType::IndexType;
using OffsetType = typename ImageType::OffsetType;
using OffsetValueType = typename ImageType::OffsetValueType;
using IndexValueType = typename ImageType::IndexValueType;
/** ComputeIndex with recursive templates */
inline static void
ComputeIndex(const IndexType & bufferedRegionIndex,
OffsetValueType offset,
[[maybe_unused]] const OffsetValueType offsetTable[],
IndexType & index)
{
static_assert(VLoop <= VImageDimension);
if constexpr (VLoop > 1)
{
constexpr unsigned int loopIndex{ VLoop - 1 };
index[loopIndex] = static_cast<IndexValueType>(offset / offsetTable[loopIndex]);
offset -= (index[loopIndex] * offsetTable[loopIndex]);
index[loopIndex] += bufferedRegionIndex[loopIndex];
ImageHelper<VImageDimension, loopIndex>::ComputeIndex(bufferedRegionIndex, offset, offsetTable, index);
}
else
{
static_assert(VLoop == 1);
// Do last
index[0] = bufferedRegionIndex[0] + static_cast<IndexValueType>(offset);
}
}
// ComputeOffset
//
inline static void
ComputeOffset(const IndexType & bufferedRegionIndex,
const IndexType & index,
[[maybe_unused]] const OffsetValueType offsetTable[],
OffsetValueType & offset)
{
static_assert(VLoop <= VImageDimension);
if constexpr (VLoop > 1)
{
constexpr unsigned int loopIndex{ VLoop - 1 };
offset += (index[loopIndex] - bufferedRegionIndex[loopIndex]) * offsetTable[loopIndex];
ImageHelper<VImageDimension, loopIndex>::ComputeOffset(bufferedRegionIndex, index, offsetTable, offset);
}
else
{
static_assert(VLoop == 1);
// Do last
offset += index[0] - bufferedRegionIndex[0];
}
}
};
} // end namespace itk
#endif
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