subtract_empty_bins.hpp

// SPDX-FileCopyrightText: 2006-2026, Knut Reinert & Freie Universität Berlin
// SPDX-FileCopyrightText: 2016-2026, Knut Reinert & MPI für molekulare Genetik
// SPDX-License-Identifier: BSD-3-Clause
 
#pragma once
 
#include <algorithm> // for clamp
#include <cmath>     // for ceil
#include <cstddef>   // for size_t
 
#include <hibf/platform.hpp>
 
namespace seqan::hibf
{
 
[[nodiscard]] constexpr size_t subtract_empty_bins(size_t const tmax, double const fraction) noexcept
{
    // There must be at least 2 technical bins available without empty bins.
    // Otherwise, there would only ever be one technical bin available.
    if (fraction == 0.0 || tmax <= 2u)
        return tmax;
 
    // `tmax * fraction` may exceed an integer by a rounding error, e.g., for the fraction `1 - subtracted / tmax` that
    // config::validate_and_set_defaults() sets. It then counts as that integer. Otherwise, a repeated
    // config::validate_and_set_defaults() could change the fraction again.
    double const rounding_error = tmax * 1e-12;
    size_t const number_of_empty_bins = std::clamp<size_t>(std::ceil(tmax * fraction - rounding_error), 1, tmax - 2);
    return tmax - number_of_empty_bins;
}
 
} // namespace seqan::hibf