TaggedPointer.h

//------------------------------------------------------------------------------
/*
    This file is part of rippled: https://github.com/ripple/rippled
    Copyright (c) 2020 Ripple Labs Inc.
 
    Permission to use, copy, modify, and/or distribute this software for any
    purpose  with  or without fee is hereby granted, provided that the above
    copyright notice and this permission notice appear in all copies.
 
    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
//==============================================================================
 
#ifndef RIPPLE_SHAMAP_TAGGEDPOINTER_H_INCLUDED
#define RIPPLE_SHAMAP_TAGGEDPOINTER_H_INCLUDED
 
#include <xrpld/shamap/SHAMapTreeNode.h>
 
#include <array>
#include <bit>
#include <cstdint>
#include <optional>
 
namespace ripple {
 
class TaggedPointer
{
    static_assert(
        alignof(SHAMapHash) >= 4,
        "Bad alignment: Tag pointer requires low two bits to be zero.");
    std::uintptr_t tp_ = 0;
    static constexpr std::uintptr_t tagMask = 3;
    static constexpr std::uintptr_t ptrMask = ~tagMask;
 
    void
    destroyHashesAndChildren();
 
    struct RawAllocateTag
    {
    };
    explicit TaggedPointer(RawAllocateTag, std::uint8_t numChildren);
 
public:
    TaggedPointer() = delete;
    explicit TaggedPointer(std::uint8_t numChildren);
 
    explicit TaggedPointer(
        TaggedPointer&& other,
        std::uint16_t isBranch,
        std::uint8_t toAllocate);
 
    explicit TaggedPointer(
        TaggedPointer&& other,
        std::uint16_t srcBranches,
        std::uint16_t dstBranches,
        std::uint8_t toAllocate);
 
    TaggedPointer(TaggedPointer const&) = delete;
 
    TaggedPointer(TaggedPointer&&);
 
    TaggedPointer&
    operator=(TaggedPointer&&);
 
    ~TaggedPointer();
 
    [[nodiscard]] std::pair<std::uint8_t, void*>
    decode() const;
 
    [[nodiscard]] std::uint8_t
    capacity() const;
 
    [[nodiscard]] bool
    isDense() const;
 
    [[nodiscard]] std::
        tuple<std::uint8_t, SHAMapHash*, std::shared_ptr<SHAMapTreeNode>*>
        getHashesAndChildren() const;
 
    [[nodiscard]] SHAMapHash*
    getHashes() const;
 
    [[nodiscard]] std::shared_ptr<SHAMapTreeNode>*
    getChildren() const;
 
    template <class F>
    void
    iterChildren(std::uint16_t isBranch, F&& f) const;
 
    template <class F>
    void
    iterNonEmptyChildIndexes(std::uint16_t isBranch, F&& f) const;
 
    std::optional<int>
    getChildIndex(std::uint16_t isBranch, int i) const;
};
 
[[nodiscard]] inline int
popcnt16(std::uint16_t a)
{
#if __cpp_lib_bitops
    return std::popcount(a);
#elif defined(__clang__) || defined(__GNUC__)
    return __builtin_popcount(a);
#else
    // fallback to table lookup
    static auto constexpr const tbl = []() {
        std::array<std::uint8_t, 256> ret{};
        for (int i = 0; i != 256; ++i)
        {
            for (int j = 0; j != 8; ++j)
            {
                if (i & (1 << j))
                    ret[i]++;
            }
        }
        return ret;
    }();
    return tbl[a & 0xff] + tbl[a >> 8];
#endif
}
 
}  // namespace ripple
 
#endif