rippled/include/xrpl/basics/Number.h

#pragma once

#include <xrpl/beast/utility/instrumentation.h>

#include <array>
#include <cstdint>
#include <functional>
#include <limits>
#include <optional>
#include <ostream>
#include <set>
#include <stdexcept>
#include <string>
#include <unordered_map>

namespace xrpl {

class Number;

std::string
to_string(Number const& amount);

template <typename T>
constexpr std::optional<int>
logTen(T value)
{
    int log = 0;
    while (value >= 10 && value % 10 == 0)
    {
        value /= 10;
        ++log;
    }
    if (value == 1)
        return log;
    return std::nullopt;
}

template <typename T>
constexpr bool
isPowerOfTen(T value)
{
    return logTen(value).has_value();
}

namespace detail {

/** Builds a table of the powers of 10
 *
 * This function is marked consteval, so it can only be run in
 * a constexpr context. This assures that it is and can only be run at
 * compile time. Doing it at runtime would be pretty wasteful and
 * inefficient.
 */
constexpr std::size_t kInt64Digits = 20;
consteval std::array<std::uint64_t, kInt64Digits>
buildPowersOfTen()
{
    std::array<std::uint64_t, kInt64Digits> result{};

    std::uint64_t power = 1;
    std::size_t exponent = 0;
    // end the loop early so it doesn't overflow;
    for (; exponent < result.size() - 1; ++exponent, power *= 10)
    {
        result[exponent] = power;
        if (power > std::numeric_limits<std::uint64_t>::max() / 10)
            throw std::logic_error("Power of 10 table is too big");
    }
    result[exponent] = power;
    if (power < std::numeric_limits<std::uint64_t>::max() / 10)
        throw std::logic_error("Power of 10 table is not big enough for the uint64_t type");

    return result;
}

}  // namespace detail

constexpr std::array<std::uint64_t, detail::kInt64Digits> kPowerOfTen = detail::buildPowersOfTen();

static_assert(kPowerOfTen[0] == 1);
static_assert(kPowerOfTen[1] == 10);
static_assert(kPowerOfTen[10] == 10'000'000'000);
static_assert(
    isPowerOfTen(kPowerOfTen.back()) && *logTen(kPowerOfTen.back()) == detail::kInt64Digits - 1);

/** MantissaRange defines a range for the mantissa of a normalized Number.
 *
 * The mantissa is in the range [min, max], where
 * * min is a power of 10, and
 * * max = min * 10 - 1.
 *
 * The MantissaScale enum indicates properties of the range: size, and some behavioral
 * options. This intentionally restricts the number of unique MantissaRanges that can
 * be instantiated: one for each scale.
 *
 * The "Small" scale is based on the behavior of STAmount for IOUs. It has a min
 * value of 10^15, and a max value of 10^16-1. This was sufficient for
 * uses before Lending Protocol was implemented, mostly related to AMM.
 *
 * However, it does not have sufficient precision to represent the full integer
 * range of int64_t values (-2^63 to 2^63-1), which are needed for XRP and MPT
 * values. The implementation of SingleAssetVault, and LendingProtocol need to
 * represent those integer values accurately and precisely, both for the
 * STNumber field type, and for internal calculations. That necessitated the
 * "large" scale.
 *
 * The "Large" scales are intended to represent all values that can be represented
 * by an STAmount - IOUs, XRP, and MPTs. It has a min value of 10^18, and a max
 * value of 10^19-1. "LargeLegacy" is like "Large", but preserves
 * a rounding error when a computation results in a mantissa of
 * Number::kMaxRep that needs to be rounded up, but rounds down
 * instead. It will maintain consistent behavior until the fixCleanup3_2_0
 * amendment is enabled.
 *
 * Note that if the mentioned amendments are eventually retired, this class
 * should be left in place, but the "Small" scale option should be removed. This
 * will allow for future expansion beyond 64-bits if it is ever needed.
 */
struct MantissaRange final
{
    using rep = std::uint64_t;

    enum class MantissaScale {
        Small,
        // LargeLegacy can be removed when fixCleanup3_2_0 is retired
        LargeLegacy,
        Large,
    };

    // This entire enum can be removed when fixCleanup3_2_0 is retired
    enum class CuspRoundingFix : bool {
        Disabled = false,
        Enabled = true,
    };

    explicit constexpr MantissaRange(MantissaScale sc) : scale(sc)
    {
    }

    MantissaScale const scale;
    int const log{getExponent(scale)};
    rep const min{getMin(scale, log)};
    rep const max{(min * 10) - 1};
    CuspRoundingFix const cuspRoundingFixEnabled{isCuspFixEnabled(scale)};

    static MantissaRange const&
    getMantissaRange(MantissaScale scale);

    static std::set<MantissaScale> const&
    getAllScales();

private:
    static constexpr int
    getExponent(MantissaScale scale)
    {
        switch (scale)
        {
            case MantissaScale::Small:
                return 15;
            case MantissaScale::LargeLegacy:
            case MantissaScale::Large:
                return 18;
            // LCOV_EXCL_START
            default:
                // If called in a constexpr context, this throw assures that the build fails if an
                // invalid scale is used.
                throw std::runtime_error("Unknown mantissa scale");
                // LCOV_EXCL_STOP
        }
    }

    // Keep this function for future use with different ways to compute
    // the ranges.
    static constexpr rep
    getMin(MantissaScale scale, int exponent)
    {
        if (exponent < 0 || exponent >= kPowerOfTen.size())
            throw std::runtime_error("Invalid exponent");  // LCOV_EXCL_LINE
        return kPowerOfTen[exponent];
    }

    static constexpr CuspRoundingFix
    isCuspFixEnabled(MantissaScale scale)
    {
        switch (scale)
        {
            case MantissaScale::Small:
            case MantissaScale::LargeLegacy:
                return CuspRoundingFix::Disabled;
            case MantissaScale::Large:
                return CuspRoundingFix::Enabled;
            default:
                // If called in a constexpr context, this throw assures that the build fails if an
                // invalid scale is used.
                throw std::runtime_error("Unknown mantissa scale");  // LCOV_EXCL_LINE
        }
    }

    static std::unordered_map<MantissaScale, MantissaRange> const&
    getRanges();
};

// Like std::integral, but only 64-bit integral types.
template <class T>
concept Integral64 = std::is_same_v<T, std::int64_t> || std::is_same_v<T, std::uint64_t>;

/** Number is a floating point type that can represent a wide range of values.
 *
 * It can represent all values that can be represented by an STAmount -
 * regardless of asset type - XRPAmount, MPTAmount, and IOUAmount, with at least
 * as much precision as those types require.
 *
 * ---- Internal Representation ----
 *
 * Internally, Number is represented with three values:
 *   1. a bool sign flag,
 *   2. a std::uint64_t mantissa,
 *   3. an int exponent.
 *
 * The internal mantissa is an unsigned integer in the range defined by the
 * current MantissaRange. The exponent is an integer in the range
 * [minExponent, maxExponent].
 *
 * See the description of MantissaRange for more details on the ranges.
 *
 * A non-zero mantissa is (almost) always normalized, meaning it and the
 * exponent are grown or shrunk until the mantissa is in the range
 * [MantissaRange.min, MantissaRange.max].
 *
 * Note:
 *   1. Normalization can be disabled by using the "unchecked" ctor tag. This
 *      should only be used at specific conversion points, some constexpr
 *      values, and in unit tests.
 *   2. The max of the "large" range, 10^19-1, is the largest 10^X-1 value that
 *      fits in an unsigned 64-bit number. (10^19-1 < 2^64-1 and
 *      10^20-1 > 2^64-1). This avoids under- and overflows.
 *
 * ---- External Interface ----
 *
 * The external interface of Number consists of a std::int64_t mantissa, which
 * is restricted to 63-bits, and an int exponent, which must be in the range
 * [minExponent, maxExponent]. The range of the mantissa depends on which
 * MantissaRange is currently active. For the "short" range, the mantissa will
 * be between 10^15 and 10^16-1. For the "large" range, the mantissa will be
 * between -(2^63-1) and 2^63-1. As noted above, the "large" range is needed to
 * represent the full range of valid XRP and MPT integer values accurately.
 *
 * Note:
 *   1. 2^63-1 is between 10^18 and 10^19-1, which are the limits of the "large"
 *      mantissa range.
 *   2. The functions mantissa() and exponent() return the external view of the
 *      Number value, specifically using a signed 63-bit mantissa. This may
 *      require altering the internal representation to fit into that range
 *      before the value is returned. The interface guarantees consistency of
 *      the two values.
 *   3. Number cannot represent -2^63 (std::numeric_limits<std::int64_t>::min())
 *      as an exact integer, but it doesn't need to, because all asset values
 *      on-ledger are non-negative. This is due to implementation details of
 *      several operations which use unsigned arithmetic internally. This is
 *      sufficient to represent all valid XRP values (where the absolute value
 *      can not exceed INITIAL_XRP: 10^17), and MPT values (where the absolute
 *      value can not exceed maxMPTokenAmount: 2^63-1).
 *
 * ---- Mantissa Range Switching ----
 *
 * The mantissa range may be changed at runtime via setMantissaScale(). The
 * default mantissa range is "large". The range is updated whenever transaction
 * processing begins, based on whether SingleAssetVault or LendingProtocol are
 * enabled. If either is enabled, the mantissa range is set to "large". If not,
 * it is set to "small", preserving backward compatibility and correct
 * "amendment-gating".
 *
 * It is extremely unlikely that any more calls to setMantissaScale() will be
 * needed outside of unit tests.
 *
 * ---- Usage With Different Ranges ----
 *
 * Outside of unit tests, and existing checks, code that uses Number should not
 * know or care which mantissa range is active.
 *
 * The results of computations using Numbers with a small mantissa may differ
 * from computations using Numbers with a large mantissa, specifically as it
 * effects the results after rounding. That is why the large mantissa range is
 * amendment gated in transaction processing.
 *
 * It is extremely unlikely that any more calls to getMantissaScale() will be
 * needed outside of unit tests.
 *
 * Code that uses Number should not assume or check anything about the
 * mantissa() or exponent() except that they fit into the "large" range
 * specified in the "External Interface" section.
 *
 * ----- Unit Tests -----
 *
 * Within unit tests, it may be useful to explicitly switch between the two
 * ranges, or to check which range is active when checking the results of
 * computations. If the test is doing the math directly, the
 * set/getMantissaScale() functions may be most appropriate. However, if the
 * test has anything to do with transaction processing, it should enable or
 * disable the amendments that control the mantissa range choice
 * (SingleAssetVault and LendingProtocol), and/or check if either of those
 * amendments are enabled to determine which result to expect.
 *
 */
class Number final
{
    using rep = std::int64_t;
    using internalrep = MantissaRange::rep;

    bool negative_{false};
    internalrep mantissa_{0};
    int exponent_{std::numeric_limits<int>::lowest()};

public:
    // The range for the exponent when normalized
    static constexpr int kMinExponent = -32768;
    static constexpr int kMaxExponent = 32768;

    static constexpr internalrep kMaxRep = std::numeric_limits<rep>::max();
    static_assert(kMaxRep == 9'223'372'036'854'775'807);
    static_assert(-kMaxRep == std::numeric_limits<rep>::min() + 1);

    // May need to make unchecked private
    struct Unchecked
    {
        explicit Unchecked() = default;
    };

    // Like unchecked, normalized is used with the ctors that take an
    // internalrep mantissa. Unlike unchecked, those ctors will normalize the
    // value.
    // Only unit tests are expected to use this class
    struct Normalized
    {
        explicit Normalized() = default;
    };

    explicit constexpr Number() = default;

    Number(rep mantissa);
    explicit Number(rep mantissa, int exponent);
    explicit constexpr Number(
        bool negative,
        internalrep mantissa,
        int exponent,
        Unchecked) noexcept;
    // Assume unsigned values are... unsigned. i.e. positive
    explicit constexpr Number(internalrep mantissa, int exponent, Unchecked) noexcept;
    // Only unit tests are expected to use this ctor
    explicit Number(bool negative, internalrep mantissa, int exponent, Normalized);
    // Assume unsigned values are... unsigned. i.e. positive
    explicit Number(internalrep mantissa, int exponent, Normalized);

    [[nodiscard]] constexpr rep
    mantissa() const noexcept;
    [[nodiscard]] constexpr int
    exponent() const noexcept;

    constexpr Number
    operator+() const noexcept;
    constexpr Number
    operator-() const noexcept;
    Number&
    operator++();
    Number
    operator++(int);
    Number&
    operator--();
    Number
    operator--(int);

    Number&
    operator+=(Number const& x);
    Number&
    operator-=(Number const& x);

    Number&
    operator*=(Number const& x);
    Number&
    operator/=(Number const& x);

    static Number
    min() noexcept;
    static Number
    max() noexcept;
    static Number
    lowest() noexcept;

    /** Conversions to Number are implicit and conversions away from Number
     *  are explicit. This design encourages and facilitates the use of Number
     *  as the preferred type for floating point arithmetic as it makes
     *  "mixed mode" more convenient, e.g. MPTAmount + Number.
     */
    explicit
    operator rep() const;  // round to nearest, even on tie

    friend constexpr bool
    operator==(Number const& x, Number const& y) noexcept
    {
        return x.negative_ == y.negative_ && x.mantissa_ == y.mantissa_ &&
            x.exponent_ == y.exponent_;
    }

    friend constexpr bool
    operator!=(Number const& x, Number const& y) noexcept
    {
        return !(x == y);
    }

    friend constexpr bool
    operator<(Number const& x, Number const& y) noexcept
    {
        // If the two amounts have different signs (zero is treated as positive)
        // then the comparison is true iff the left is negative.
        bool const lneg = x.negative_;
        bool const rneg = y.negative_;

        if (lneg != rneg)
            return lneg;

        // Both have same sign and the left is zero: the right must be
        // greater than 0.
        if (x.mantissa_ == 0)
            return y.mantissa_ > 0;

        // Both have same sign, the right is zero and the left is non-zero.
        if (y.mantissa_ == 0)
            return false;

        // Both have the same sign, compare by exponents:
        if (x.exponent_ > y.exponent_)
            return lneg;
        if (x.exponent_ < y.exponent_)
            return !lneg;

        // If equal exponents, compare mantissas
        return x.mantissa_ < y.mantissa_;
    }

    /** Return the sign of the amount */
    [[nodiscard]] constexpr int
    signum() const noexcept
    {
        if (negative_)
            return -1;
        return (mantissa_ != 0u) ? 1 : 0;
    }

    [[nodiscard]] Number
    truncate() const noexcept;

    friend constexpr bool
    operator>(Number const& x, Number const& y) noexcept
    {
        return y < x;
    }

    friend constexpr bool
    operator<=(Number const& x, Number const& y) noexcept
    {
        return !(y < x);
    }

    friend constexpr bool
    operator>=(Number const& x, Number const& y) noexcept
    {
        return !(x < y);
    }

    friend std::ostream&
    operator<<(std::ostream& os, Number const& x)
    {
        return os << to_string(x);
    }

    friend std::string
    to_string(Number const& amount);

    friend Number
    root(Number f, unsigned d);

    friend Number
    root2(Number f);

    // Thread local rounding control.  Default is to_nearest
    enum class RoundingMode { ToNearest, TowardsZero, Downward, Upward };

    static RoundingMode
    getround();

    static RoundingMode
    setround(RoundingMode inMode);

    /** Returns which mantissa scale is currently in use for normalization.
     *
     * If you think you need to call this outside of unit tests, no you don't.
     */
    static MantissaRange::MantissaScale
    getMantissaScale();

    /** Changes which mantissa scale is used for normalization.
     *
     * If you think you need to call this outside of unit tests, no you don't.
     */
    static void
    setMantissaScale(MantissaRange::MantissaScale scale);

    static internalrep
    minMantissa()
    {
        return kRange.get().min;
    }

    static internalrep
    maxMantissa()
    {
        return kRange.get().max;
    }

    static int
    mantissaLog()
    {
        return kRange.get().log;
    }

    static Number
    one();

    template <
        auto MinMantissa,
        auto MaxMantissa,
        Integral64 T = std::decay_t<decltype(MinMantissa)>>
    [[nodiscard]]
    std::pair<T, int>
    normalizeToRange() const;

private:
    static thread_local RoundingMode mode;
    // The available ranges for mantissa

    // The range for the mantissa when normalized.
    // Use reference_wrapper to avoid making copies, and prevent accidentally
    // changing the values inside the range.
    static thread_local std::reference_wrapper<MantissaRange const> kRange;

    void
    normalize(MantissaRange const& range);

    /** Normalize Number components to an arbitrary range.
     *
     * min/maxMantissa are parameters because this function is used by both
     * normalize(), which reads from kRange, and by normalizeToRange,
     * which is public and can accept an arbitrary range from the caller.
     */
    template <class T>
    static void
    normalize(
        bool& negative,
        T& mantissa,
        int& exponent,
        internalrep const& minMantissa,
        internalrep const& maxMantissa,
        MantissaRange::CuspRoundingFix cuspRoundingFixEnabled);

    template <class T>
    friend void
    doNormalize(
        bool& negative,
        T& mantissa,
        int& exponent,
        MantissaRange::rep const& minMantissa,
        MantissaRange::rep const& maxMantissa,
        MantissaRange::CuspRoundingFix cuspRoundingFixEnabled,
        bool dropped);

    [[nodiscard]] bool
    isnormal() const noexcept;

    // Copy the number, but modify the exponent by "exponentDelta". Because the
    // mantissa doesn't change, the result will be "mostly" normalized, but the
    // exponent could go out of range, so it will be checked.
    [[nodiscard]] Number
    shiftExponent(int exponentDelta) const;

    // Safely convert rep (int64) mantissa to internalrep (uint64). If the rep
    // is negative, returns the positive value. This takes a little extra work
    // because converting std::numeric_limits<std::int64_t>::min() flirts with
    // UB, and can vary across compilers.
    static internalrep
    externalToInternal(rep mantissa);

    class Guard;
};

constexpr Number::Number(bool negative, internalrep mantissa, int exponent, Unchecked) noexcept
    : negative_(negative), mantissa_{mantissa}, exponent_{exponent}
{
}

constexpr Number::Number(internalrep mantissa, int exponent, Unchecked) noexcept
    : Number(false, mantissa, exponent, Unchecked{})
{
}

static constexpr Number kNumZero{};

inline Number::Number(bool negative, internalrep mantissa, int exponent, Normalized)
    : Number(negative, mantissa, exponent, Unchecked{})
{
    normalize(kRange);
}

inline Number::Number(internalrep mantissa, int exponent, Normalized)
    : Number(false, mantissa, exponent, Normalized{})
{
}

inline Number::Number(rep mantissa, int exponent)
    : Number(mantissa < 0, externalToInternal(mantissa), exponent, Normalized{})
{
}

inline Number::Number(rep mantissa) : Number{mantissa, 0}
{
}

/** Returns the mantissa of the external view of the Number.
 *
 * Please see the "---- External Interface ----" section of the class
 * documentation for an explanation of why the internal value may be modified.
 */
constexpr Number::rep
Number::mantissa() const noexcept
{
    auto m = mantissa_;
    if (m > kMaxRep)
    {
        XRPL_ASSERT_PARTS(
            !isnormal() || (m % 10 == 0 && m / 10 <= kMaxRep),
            "xrpl::Number::mantissa",
            "large normalized mantissa has no remainder");
        m /= 10;
    }
    auto const sign = negative_ ? -1 : 1;
    return sign * static_cast<Number::rep>(m);
}

/** Returns the exponent of the external view of the Number.
 *
 * Please see the "---- External Interface ----" section of the class
 * documentation for an explanation of why the internal value may be modified.
 */
constexpr int
Number::exponent() const noexcept
{
    auto e = exponent_;
    if (mantissa_ > kMaxRep)
    {
        XRPL_ASSERT_PARTS(
            !isnormal() || (mantissa_ % 10 == 0 && mantissa_ / 10 <= kMaxRep),
            "xrpl::Number::exponent",
            "large normalized mantissa has no remainder");
        ++e;
    }
    return e;
}

constexpr Number
Number::operator+() const noexcept
{
    return *this;
}

constexpr Number
Number::operator-() const noexcept
{
    if (mantissa_ == 0)
        return Number{};
    auto x = *this;
    x.negative_ = !x.negative_;
    return x;
}

inline Number&
Number::operator++()
{
    *this += one();
    return *this;
}

inline Number
Number::operator++(int)
{
    auto x = *this;
    ++(*this);
    return x;
}

inline Number&
Number::operator--()
{
    *this -= one();
    return *this;
}

inline Number
Number::operator--(int)
{
    auto x = *this;
    --(*this);
    return x;
}

inline Number&
Number::operator-=(Number const& x)
{
    return *this += -x;
}

inline Number
operator+(Number const& x, Number const& y)
{
    auto z = x;
    z += y;
    return z;
}

inline Number
operator-(Number const& x, Number const& y)
{
    auto z = x;
    z -= y;
    return z;
}

inline Number
operator*(Number const& x, Number const& y)
{
    auto z = x;
    z *= y;
    return z;
}

inline Number
operator/(Number const& x, Number const& y)
{
    auto z = x;
    z /= y;
    return z;
}

inline Number
Number::min() noexcept
{
    return Number{false, kRange.get().min, kMinExponent, Unchecked{}};
}

inline Number
Number::max() noexcept
{
    return Number{false, std::min(kRange.get().max, kMaxRep), kMaxExponent, Unchecked{}};
}

inline Number
Number::lowest() noexcept
{
    return Number{true, std::min(kRange.get().max, kMaxRep), kMaxExponent, Unchecked{}};
}

inline bool
Number::isnormal() const noexcept
{
    MantissaRange const& range = kRange;
    auto const absM = mantissa_;
    return *this == Number{} ||
        (range.min <= absM && absM <= range.max && (absM <= kMaxRep || absM % 10 == 0) &&
         kMinExponent <= exponent_ && exponent_ <= kMaxExponent);
}

template <auto MinMantissa, auto MaxMantissa, Integral64 T>
std::pair<T, int>
Number::normalizeToRange() const
{
    static_assert(std::is_same_v<T, std::uint64_t> || std::is_same_v<T, std::int64_t>);
    static_assert(std::is_same_v<T, std::decay_t<decltype(MinMantissa)>>);
    static_assert(std::is_same_v<T, std::decay_t<decltype(MaxMantissa)>>);
    auto constexpr kMIN = static_cast<T>(MinMantissa);
    auto constexpr kMAX = static_cast<T>(MaxMantissa);
    static_assert(kMIN > 0);
    static_assert(kMIN % 10 == 0);
    static_assert(isPowerOfTen(kMIN));
    static_assert(kMAX % 10 == 9);
    static_assert((kMAX + 1) / 10 == kMIN);

    bool negative = negative_;
    internalrep mantissa = mantissa_;
    int exponent = exponent_;

    if constexpr (std::is_unsigned_v<T>)
    {
        XRPL_ASSERT_PARTS(
            !negative,
            "xrpl::Number::normalizeToRange",
            "Number is non-negative for unsigned range.");
    }
    // Don't need to worry about the cuspRounding fix because rounding up will never take the
    // mantissa over maxMantissa with a ones digit value other than 0. 0 can safely be truncated.
    Number::normalize(
        negative, mantissa, exponent, kMIN, kMAX, MantissaRange::CuspRoundingFix::Disabled);

    auto const sign = negative ? -1 : 1;
    return std::make_pair(static_cast<T>(sign * mantissa), exponent);
}

constexpr Number
abs(Number x) noexcept
{
    if (x < Number{})
        x = -x;
    return x;
}

// Returns f^n
// Uses a log_2(n) number of multiplications

Number
power(Number const& f, unsigned n);

// Returns f^(1/d)
// Uses Newton–Raphson iterations until the result stops changing
// to find the root of the polynomial g(x) = x^d - f

Number
root(Number f, unsigned d);

Number
root2(Number f);

// Returns f^(n/d)

Number
power(Number const& f, unsigned n, unsigned d);

// Return 0 if abs(x) < limit, else returns x

constexpr Number
squelch(Number const& x, Number const& limit) noexcept
{
    if (abs(x) < limit)
        return Number{};
    return x;
}

inline std::string
to_string(MantissaRange::MantissaScale const& scale)
{
    switch (scale)
    {
        case MantissaRange::MantissaScale::Small:
            return "small";
        case MantissaRange::MantissaScale::LargeLegacy:
            return "largeLegacy";
        case MantissaRange::MantissaScale::Large:
            return "large";
        default:
            throw std::runtime_error("Bad scale");
    }
}

class SaveNumberRoundMode
{
    Number::RoundingMode mode_;

public:
    ~SaveNumberRoundMode()
    {
        Number::setround(mode_);
    }
    explicit SaveNumberRoundMode(Number::RoundingMode mode) noexcept : mode_{mode}
    {
    }
    SaveNumberRoundMode(SaveNumberRoundMode const&) = delete;
    SaveNumberRoundMode&
    operator=(SaveNumberRoundMode const&) = delete;
};

// saveNumberRoundMode doesn't do quite enough for us.  What we want is a
// Number::RoundModeGuard that sets the new mode and restores the old mode
// when it leaves scope.  Since Number doesn't have that facility, we'll
// build it here.
class NumberRoundModeGuard
{
    SaveNumberRoundMode saved_;

public:
    explicit NumberRoundModeGuard(Number::RoundingMode mode) noexcept
        : saved_{Number::setround(mode)}
    {
    }

    NumberRoundModeGuard(NumberRoundModeGuard const&) = delete;

    NumberRoundModeGuard&
    operator=(NumberRoundModeGuard const&) = delete;
};

/** Sets the new scale and restores the old scale when it leaves scope.
 *
 * If you think you need to use this class outside of unit tests, no you don't.
 *
 */
class NumberMantissaScaleGuard
{
    MantissaRange::MantissaScale const saved_;

public:
    explicit NumberMantissaScaleGuard(MantissaRange::MantissaScale scale) noexcept
        : saved_{Number::getMantissaScale()}
    {
        Number::setMantissaScale(scale);
    }

    ~NumberMantissaScaleGuard()
    {
        Number::setMantissaScale(saved_);
    }

    NumberMantissaScaleGuard(NumberMantissaScaleGuard const&) = delete;

    NumberMantissaScaleGuard&
    operator=(NumberMantissaScaleGuard const&) = delete;
};

}  // namespace xrpl