rippled/src/ripple/ledger/CashDiff.h

//------------------------------------------------------------------------------
/*
    This file is part of rippled: https://github.com/ripple/rippled
    Copyright (c) 2016 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_LEDGER_CASHDIFF_H_INCLUDED
#define RIPPLE_LEDGER_CASHDIFF_H_INCLUDED

#include <ripple/basics/safe_cast.h>
#include <ripple/protocol/STAmount.h>
#include <memory>  // std::unique_ptr

namespace ripple {

class ReadView;

namespace detail {

class ApplyStateTable;

}

// Used by CashDiff to specify filters applied while processing differences.
// Entries are bit flags that can be ANDed and ORed.
enum class CashFilter : std::uint8_t {
    none = 0x0,
    treatZeroOfferAsDeletion = 0x1
};
inline CashFilter
operator|(CashFilter lhs, CashFilter rhs)
{
    using ul_t = std::underlying_type<CashFilter>::type;
    return static_cast<CashFilter>(safe_cast<ul_t>(lhs) | safe_cast<ul_t>(rhs));
}
inline CashFilter
operator&(CashFilter lhs, CashFilter rhs)
{
    using ul_t = std::underlying_type<CashFilter>::type;
    return static_cast<CashFilter>(safe_cast<ul_t>(lhs) & safe_cast<ul_t>(rhs));
}

//------------------------------------------------------------------------------

// A class to identify differences between two ApplyStateTable instances
// for debugging.
class CashDiff
{
public:
    CashDiff() = delete;
    CashDiff(CashDiff const&) = delete;
    CashDiff(CashDiff&& other) noexcept;
    CashDiff&
    operator=(CashDiff const&) = delete;
    ~CashDiff();

    CashDiff(
        ReadView const& view,
        CashFilter lhsFilter,
        detail::ApplyStateTable const& lhs,
        CashFilter rhsFilter,
        detail::ApplyStateTable const& rhs);

    // Returns the number of cases where lhs and rhs had the same entries
    // (but not necessarily the same amounts)
    std::size_t
    commonCount() const;

    // Returns the number of entries that were present in rhs but not in lhs.
    std::size_t
    rhsOnlyCount() const;

    // Returns the number of entries that were present in lhs but not in rhs.
    std::size_t
    lhsOnlyCount() const;

    // Returns true is there are any differences to report.
    bool
    hasDiff() const;

    // Checks for the XRP round-to-zero case.  Returns zero if not detected.
    // Otherwise returns -1 if seen on lhs, +1 if seen on rhs.
    //
    // For tiny offers of TakerPays IOU and TakerGets XRP, cases have been
    // observed where XRP rounding allows a tiny amount of IOU to be
    // removed from an Offer while returning no XRP to the offer owner.
    // That's because the XRP amount was rounded down to zero drops.
    //
    // The person submitting the tiny offer does not, however, get something
    // for nothing.  The transaction's fee is significantly larger than the
    // value of the received IOU.
    //
    // This check should be made before calling rmDust().
    int
    xrpRoundToZero() const;

    // Remove dust-sized differences.  Returns true is dust was removed.
    bool
    rmDust();

    // Remove offer deletion differences from a given side.  Returns true
    // if any deleted offers were removed from the differences.
    bool
    rmLhsDeletedOffers();
    bool
    rmRhsDeletedOffers();

    struct OfferAmounts
    {
        static std::size_t constexpr count_ = 2;
        static std::size_t constexpr count()
        {
            return count_;
        }
        STAmount amounts[count_];
        STAmount const&
        takerPays() const
        {
            return amounts[0];
        }
        STAmount const&
        takerGets() const
        {
            return amounts[1];
        }
        STAmount const&
        operator[](std::size_t i) const
        {
            assert(i < count());
            return amounts[i];
        }
        friend bool
        operator<(OfferAmounts const& lhs, OfferAmounts const& rhs)
        {
            if (lhs[0] < rhs[0])
                return true;
            if (lhs[0] > rhs[0])
                return false;
            return lhs[1] < rhs[1];
        }
    };

private:
    class Impl;
    std::unique_ptr<Impl> impl_;
};

// Return true if the difference between two STAmounts is "small".
//
// If v1 and v2 have different issues, then their difference is never dust.
// If v1 < v2, smallness is computed as v1 / (v2 - v1).
// The e10 argument says at least how big that ratio must be.  Default is 10^6.
// If both v1 and v2 are XRP, consider any diff of 2 drops or less to be dust.
bool
diffIsDust(STAmount const& v1, STAmount const& v2, std::uint8_t e10 = 6);

}  // namespace ripple

#endif