align.hpp

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// SPDX-License-Identifier: BSL-1.0
// SPDX-FileCopyrightText: Copyright (C) 2020 Tobias Hienzsch
 
#ifndef TETL_MEMORY_ALIGN_HPP
#define TETL_MEMORY_ALIGN_HPP
 
#include <etl/_bit/bit_cast.hpp>
#include <etl/_cstddef/size_t.hpp>
#include <etl/_cstdint/uintptr_t.hpp>
 
namespace etl {
 
/// \brief Given a pointer ptr to a buffer of size space, returns a pointer
/// aligned by the specified alignment for size number of bytes and decreases
/// space argument by the number of bytes used for alignment. The first aligned
/// address is returned.
///
/// The function modifies the pointer only if it would be possible to fit the
/// wanted number of bytes aligned by the given alignment into the buffer. If
/// the buffer is too small, the function does nothing and returns nullptr.
///
/// \warning The behavior is undefined if alignment is not a power of two.
[[nodiscard]] inline auto align(etl::size_t alignment, etl::size_t size, void*& ptr, etl::size_t& space) noexcept
    -> void*
{
    auto off = static_cast<etl::size_t>(bit_cast<etl::uintptr_t>(ptr) & (alignment - 1));
    if (off != 0) {
        off = alignment - off;
    }
    if (space < off or space - off < size) {
        return nullptr;
    }
 
    ptr = static_cast<char*>(ptr) + off;
    space -= off;
    return ptr;
}
 
} // namespace etl
 
#endif // TETL_MEMORY_ALIGN_HPP