for_each_block.cpp

// Copyright (C) The DDC development team, see COPYRIGHT.md file
//
// SPDX-License-Identifier: MIT
 
#include <cassert>
#include <cstddef>
#include <span>
#include <stdexcept>
 
#include "discrete_vector.hpp"
#include "for_each_block.hpp"
 
namespace {
 
bool is_power_of_2(std::size_t const n) noexcept
{
    return n > 0 && !(n & (n - 1));
}
 
} // namespace
 
namespace ddc::detail {
 
void distribute_blocks(
        std::size_t nb_blocks,
        std::span<DiscreteVectorElement const> const sizes,
        std::span<DiscreteVectorElement> const nb_blocks_per_dim)
{
    assert(sizes.size() == nb_blocks_per_dim.size());
 
    if (!is_power_of_2(nb_blocks)) {
        throw std::runtime_error("DDC distribute_blocks expects a power of 2.");
    }
 
    for (DiscreteVectorElement& blocks : nb_blocks_per_dim) {
        blocks = 1;
    }
 
    std::size_t dim = 0;
    while (nb_blocks != 1) {
        if (dim >= sizes.size()) {
            throw std::runtime_error("DDC expects a smaller number of blocks.");
        }
 
        if (sizes[dim] >= nb_blocks_per_dim[dim] * 2) {
            nb_blocks_per_dim[dim] *= 2;
            nb_blocks /= 2;
        } else {
            ++dim;
        }
    }
}
 
ComputeBlockFn::ComputeBlockFn(
        DiscreteVectorElement const extent,
        DiscreteVectorElement const nb_blocks) noexcept
    : m_quot(extent / nb_blocks)
    , m_rem(extent % nb_blocks)
{
}
 
DiscreteVectorElement ComputeBlockFn::operator()(DiscreteVectorElement const i) const noexcept
{
    if (i < m_rem) {
        return m_quot + 1;
    }
    return m_quot;
}
 
} // namespace ddc::detail