pick_nd_block_dimensions.hpp

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#ifndef RITSUKO_PICK_ND_BLOCK_DIMENSIONS_HPP
#define RITSUKO_PICK_ND_BLOCK_DIMENSIONS_HPP
 
#include "H5Cpp.h"
 
namespace ritsuko {
 
namespace hdf5 {
 
inline std::vector<hsize_t> pick_nd_block_dimensions(const H5::DSetCreatPropList& cplist, const std::vector<hsize_t>& dimensions, hsize_t buffer_size = 10000) {
    size_t ndims = dimensions.size();
    std::vector<hsize_t> chunk_extent(ndims, 1);
    if (cplist.getLayout() == H5D_CHUNKED) {
        cplist.getChunk(chunk_extent.size(), chunk_extent.data());
    }
 
    // Scaling up the block size as much as possible. We start from the
    // fastest-changing dimension (i.e., the last one in HDF5) and increase it,
    // and then we move onto the next-fastest dimension, and so on until the
    // buffer size is exhausted.
    auto block_extent = chunk_extent;
    hsize_t block_size = 1;
    for (hsize_t d = 0; d < ndims; ++d) {
        block_extent[d] = std::min(block_extent[d], dimensions[d]); // should be a no-op, but we do this just in case.
        block_size *= block_extent[d];
    }
 
    if (block_size) {
        for (hsize_t i = ndims; i > 0; --i) {
            int multiple = buffer_size / block_size;
            if (multiple <= 1) {
                break;
            }
            auto d = i - 1;
            block_size /= block_extent[d];
            block_extent[d] = std::min(dimensions[d], block_extent[d] * multiple);
            block_size *= block_extent[d];
        }
    } else {
        std::fill(block_extent.begin(), block_extent.end(), 0);
    }
 
    return block_extent;
}
 
}
 
}
 
#endif