SlabCacheStats.hpp

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#ifndef TATAMI_CHUNKED_SLAB_CACHE_STATS_HPP
#define TATAMI_CHUNKED_SLAB_CACHE_STATS_HPP
 
#include <algorithm>
#include <cstddef>
 
#include "sanisizer/sanisizer.hpp"
 
namespace tatami_chunked {
 
template<typename Index_>
Index_ compute_max_slabs_in_cache(std::size_t slab_size_in_elements, Index_ num_slabs, std::size_t cache_size_in_elements, bool require_minimum_cache) {
    if (slab_size_in_elements == 0) {
        return num_slabs;
    }
 
    auto tmp = cache_size_in_elements / slab_size_in_elements;
    if (tmp == 0 && require_minimum_cache) {
        return 1;
    } 
 
    return sanisizer::min(tmp, num_slabs);
}
template<typename Index_>
struct SlabCacheStats {
    std::size_t slab_size_in_elements;
 
    Index_ max_slabs_in_cache;
 
    SlabCacheStats(Index_ target_length, Index_ non_target_length, Index_ target_num_slabs, std::size_t cache_size_in_elements, bool require_minimum_cache) :
        // Don't be tempted to do unsafe casts of target_length to size_t, as a smaller type could allow us to sip the overflow check for the product.
        // Also, this class might be used outside of the tatami::Matrix contract (i.e., Index_ might store values beyond std::size_t).
        slab_size_in_elements(sanisizer::product<std::size_t>(target_length, non_target_length)),
        max_slabs_in_cache(compute_max_slabs_in_cache(slab_size_in_elements, target_num_slabs, cache_size_in_elements, require_minimum_cache))
    {}
 
    SlabCacheStats(Index_ target_length, Index_ non_target_length, Index_ target_num_slabs, std::size_t cache_size_in_bytes, std::size_t element_size, bool require_minimum_cache) :
        slab_size_in_elements(sanisizer::product<std::size_t>(target_length, non_target_length)),
        max_slabs_in_cache([&]{
            if (element_size == 0) {
                return target_num_slabs;
            } else {
                return compute_max_slabs_in_cache(slab_size_in_elements, target_num_slabs, cache_size_in_bytes / element_size, require_minimum_cache); 
            }
        }())
    {}
};
 
}
 
#endif