byte_format.hpp

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#ifndef RPNXQUERYGRAPH_BYTE_FORMAT_HPP
#define RPNXQUERYGRAPH_BYTE_FORMAT_HPP

 
#include <algorithm>
#include <cmath>
#include <cstddef>
#include <iomanip>
#include <sstream>
#include <string>
 
namespace rpnx::querygraph
{
    inline std::string format_iec_bytes(std::size_t bytes)
    {
        static constexpr const char* units[] = {"B", "KiB", "MiB", "GiB", "TiB", "PiB", "EiB"};
        static constexpr std::size_t unit_count = sizeof(units) / sizeof(units[0]);
 
        if (bytes == 0)
        {
            return "0B";
        }
 
        double value = static_cast< double >(bytes);
        std::size_t unit_index = 0;
        while (value >= 1024.0 && unit_index + 1 < unit_count)
        {
            value /= 1024.0;
            ++unit_index;
        }
 
        auto decimals_for = [](double v) -> std::ptrdiff_t
        {
            if (v <= 0.0)
            {
                return 0;
            }
            auto const digits = static_cast< std::ptrdiff_t >(std::floor(std::log10(v))) + 1;
            return std::max< std::ptrdiff_t >(0, 3 - digits);
        };
 
        auto decimals = decimals_for(value);
        double scale = std::pow(10.0, static_cast< double >(decimals));
        double rounded = std::round(value * scale) / scale;
 
        if (rounded >= 1024.0 && unit_index + 1 < unit_count)
        {
            value = rounded / 1024.0;
            ++unit_index;
            decimals = decimals_for(value);
            scale = std::pow(10.0, static_cast< double >(decimals));
            rounded = std::round(value * scale) / scale;
        }
 
        std::ostringstream oss;
        if (unit_index == 0)
        {
            oss << bytes << units[unit_index];
            return oss.str();
        }
 
        oss << std::fixed << std::setprecision(static_cast< int >(decimals)) << rounded << units[unit_index];
        return oss.str();
    }
} // namespace rpnx::querygraph
 
#endif // RPNXQUERYGRAPH_BYTE_FORMAT_HPP