rippled/src/ripple/basics/impl/IOUAmount.cpp

//------------------------------------------------------------------------------
/*
    This file is part of rippled: https://github.com/ripple/rippled
    Copyright (c) 2012, 2013 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.
*/
//==============================================================================

#include <ripple/basics/IOUAmount.h>
#include <ripple/basics/contract.h>
#include <boost/multiprecision/cpp_int.hpp>
#include <algorithm>
#include <iterator>
#include <numeric>
#include <stdexcept>

namespace ripple {

namespace {

// Use a static inside a function to help prevent order-of-initialzation issues
LocalValue<bool>&
getStaticSTNumberSwitchover()
{
    static LocalValue<bool> r{true};
    return r;
}
}  // namespace

bool
getSTNumberSwitchover()
{
    return *getStaticSTNumberSwitchover();
}

void
setSTNumberSwitchover(bool v)
{
    *getStaticSTNumberSwitchover() = v;
}

/* The range for the mantissa when normalized */
static std::int64_t constexpr minMantissa = 1000000000000000ull;
static std::int64_t constexpr maxMantissa = 9999999999999999ull;
/* The range for the exponent when normalized */
static int constexpr minExponent = -96;
static int constexpr maxExponent = 80;

IOUAmount
IOUAmount::minPositiveAmount()
{
    return IOUAmount(minMantissa, minExponent);
}

void
IOUAmount::normalize()
{
    if (mantissa_ == 0)
    {
        *this = beast::zero;
        return;
    }

    if (getSTNumberSwitchover())
    {
        Number const v{mantissa_, exponent_};
        mantissa_ = v.mantissa();
        exponent_ = v.exponent();
        if (exponent_ > maxExponent)
            Throw<std::overflow_error>("value overflow");
        if (exponent_ < minExponent)
            *this = beast::zero;
        return;
    }

    bool const negative = (mantissa_ < 0);

    if (negative)
        mantissa_ = -mantissa_;

    while ((mantissa_ < minMantissa) && (exponent_ > minExponent))
    {
        mantissa_ *= 10;
        --exponent_;
    }

    while (mantissa_ > maxMantissa)
    {
        if (exponent_ >= maxExponent)
            Throw<std::overflow_error>("IOUAmount::normalize");

        mantissa_ /= 10;
        ++exponent_;
    }

    if ((exponent_ < minExponent) || (mantissa_ < minMantissa))
    {
        *this = beast::zero;
        return;
    }

    if (exponent_ > maxExponent)
        Throw<std::overflow_error>("value overflow");

    if (negative)
        mantissa_ = -mantissa_;
}

IOUAmount::IOUAmount(Number const& other)
    : mantissa_(other.mantissa()), exponent_(other.exponent())
{
    if (exponent_ > maxExponent)
        Throw<std::overflow_error>("value overflow");
    if (exponent_ < minExponent)
        *this = beast::zero;
}

IOUAmount&
IOUAmount::operator+=(IOUAmount const& other)
{
    if (other == beast::zero)
        return *this;

    if (*this == beast::zero)
    {
        *this = other;
        return *this;
    }

    if (getSTNumberSwitchover())
    {
        *this = IOUAmount{Number{*this} + Number{other}};
        return *this;
    }
    auto m = other.mantissa_;
    auto e = other.exponent_;

    while (exponent_ < e)
    {
        mantissa_ /= 10;
        ++exponent_;
    }

    while (e < exponent_)
    {
        m /= 10;
        ++e;
    }

    // This addition cannot overflow an std::int64_t but we may throw from
    // normalize if the result isn't representable.
    mantissa_ += m;

    if (mantissa_ >= -10 && mantissa_ <= 10)
    {
        *this = beast::zero;
        return *this;
    }

    normalize();
    return *this;
}

std::string
to_string(IOUAmount const& amount)
{
    return to_string(Number{amount});
}

IOUAmount
mulRatio(
    IOUAmount const& amt,
    std::uint32_t num,
    std::uint32_t den,
    bool roundUp)
{
    using namespace boost::multiprecision;

    if (!den)
        Throw<std::runtime_error>("division by zero");

    // A vector with the value 10^index for indexes from 0 to 29
    // The largest intermediate value we expect is 2^96, which
    // is less than 10^29
    static auto const powerTable = [] {
        std::vector<uint128_t> result;
        result.reserve(30);  // 2^96 is largest intermediate result size
        uint128_t cur(1);
        for (int i = 0; i < 30; ++i)
        {
            result.push_back(cur);
            cur *= 10;
        };
        return result;
    }();

    // Return floor(log10(v))
    // Note: Returns -1 for v == 0
    static auto log10Floor = [](uint128_t const& v) {
        // Find the index of the first element >= the requested element, the
        // index is the log of the element in the log table.
        auto const l =
            std::lower_bound(powerTable.begin(), powerTable.end(), v);
        int index = std::distance(powerTable.begin(), l);
        // If we're not equal, subtract to get the floor
        if (*l != v)
            --index;
        return index;
    };

    // Return ceil(log10(v))
    static auto log10Ceil = [](uint128_t const& v) {
        // Find the index of the first element >= the requested element, the
        // index is the log of the element in the log table.
        auto const l =
            std::lower_bound(powerTable.begin(), powerTable.end(), v);
        return int(std::distance(powerTable.begin(), l));
    };

    static auto const fl64 =
        log10Floor(std::numeric_limits<std::int64_t>::max());

    bool const neg = amt.mantissa() < 0;
    uint128_t const den128(den);
    // a 32 value * a 64 bit value and stored in a 128 bit value. This will
    // never overflow
    uint128_t const mul =
        uint128_t(neg ? -amt.mantissa() : amt.mantissa()) * uint128_t(num);

    auto low = mul / den128;
    uint128_t rem(mul - low * den128);

    int exponent = amt.exponent();

    if (rem)
    {
        // Mathematically, the result is low + rem/den128. However, since this
        // uses integer division rem/den128 will be zero. Scale the result so
        // low does not overflow the largest amount we can store in the mantissa
        // and (rem/den128) is as large as possible. Scale by multiplying low
        // and rem by 10 and subtracting one from the exponent. We could do this
        // with a loop, but it's more efficient to use logarithms.
        auto const roomToGrow = fl64 - log10Ceil(low);
        if (roomToGrow > 0)
        {
            exponent -= roomToGrow;
            low *= powerTable[roomToGrow];
            rem *= powerTable[roomToGrow];
        }
        auto const addRem = rem / den128;
        low += addRem;
        rem = rem - addRem * den128;
    }

    // The largest result we can have is ~2^95, which overflows the 64 bit
    // result we can store in the mantissa. Scale result down by dividing by ten
    // and adding one to the exponent until the low will fit in the 64-bit
    // mantissa. Use logarithms to avoid looping.
    bool hasRem = bool(rem);
    auto const mustShrink = log10Ceil(low) - fl64;
    if (mustShrink > 0)
    {
        uint128_t const sav(low);
        exponent += mustShrink;
        low /= powerTable[mustShrink];
        if (!hasRem)
            hasRem = bool(sav - low * powerTable[mustShrink]);
    }

    std::int64_t mantissa = low.convert_to<std::int64_t>();

    // normalize before rounding
    if (neg)
        mantissa *= -1;

    IOUAmount result(mantissa, exponent);

    if (hasRem)
    {
        // handle rounding
        if (roundUp && !neg)
        {
            if (!result)
            {
                return IOUAmount::minPositiveAmount();
            }
            // This addition cannot overflow because the mantissa is already
            // normalized
            return IOUAmount(result.mantissa() + 1, result.exponent());
        }

        if (!roundUp && neg)
        {
            if (!result)
            {
                return IOUAmount(-minMantissa, minExponent);
            }
            // This subtraction cannot underflow because `result` is not zero
            return IOUAmount(result.mantissa() - 1, result.exponent());
        }
    }

    return result;
}

}  // namespace ripple