feefrac.h

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// Copyright (c) The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
#ifndef BITCOIN_UTIL_FEEFRAC_H
#define BITCOIN_UTIL_FEEFRAC_H
 
#include <stdint.h>
#include <compare>
#include <vector>
#include <span.h>
#include <util/check.h>
 
struct FeeFrac
{
    static inline std::pair<int64_t, uint32_t> MulFallback(int64_t a, int32_t b) noexcept
    {
        // Otherwise, emulate 96-bit multiplication using two 64-bit multiplies.
        int64_t low = int64_t{static_cast<uint32_t>(a)} * b;
        int64_t high = (a >> 32) * b;
        return {high + (low >> 32), static_cast<uint32_t>(low)};
    }
 
    // Compute a * b, returning an unspecified but totally ordered type.
#ifdef __SIZEOF_INT128__
    static inline __int128 Mul(int64_t a, int32_t b) noexcept
    {
        // If __int128 is available, use 128-bit wide multiply.
        return __int128{a} * b;
    }
#else
    static constexpr auto Mul = MulFallback;
#endif
 
    int64_t fee;
    int32_t size;
 
    constexpr inline FeeFrac() noexcept : fee{0}, size{0} {}
 
    constexpr inline FeeFrac(int64_t f, int32_t s) noexcept : fee{f}, size{s} {}
 
    constexpr inline FeeFrac(const FeeFrac&) noexcept = default;
    constexpr inline FeeFrac& operator=(const FeeFrac&) noexcept = default;
 
    bool inline IsEmpty() const noexcept {
        return size == 0;
    }
 
    void inline operator+=(const FeeFrac& other) noexcept
    {
        fee += other.fee;
        size += other.size;
    }
 
    void inline operator-=(const FeeFrac& other) noexcept
    {
        fee -= other.fee;
        size -= other.size;
    }
 
    friend inline FeeFrac operator+(const FeeFrac& a, const FeeFrac& b) noexcept
    {
        return {a.fee + b.fee, a.size + b.size};
    }
 
    friend inline FeeFrac operator-(const FeeFrac& a, const FeeFrac& b) noexcept
    {
        return {a.fee - b.fee, a.size - b.size};
    }
 
    friend inline bool operator==(const FeeFrac& a, const FeeFrac& b) noexcept
    {
        return a.fee == b.fee && a.size == b.size;
    }
 
    friend inline std::weak_ordering FeeRateCompare(const FeeFrac& a, const FeeFrac& b) noexcept
    {
        auto cross_a = Mul(a.fee, b.size), cross_b = Mul(b.fee, a.size);
        return cross_a <=> cross_b;
    }
 
    friend inline bool operator<<(const FeeFrac& a, const FeeFrac& b) noexcept
    {
        auto cross_a = Mul(a.fee, b.size), cross_b = Mul(b.fee, a.size);
        return cross_a < cross_b;
    }
 
    friend inline bool operator>>(const FeeFrac& a, const FeeFrac& b) noexcept
    {
        auto cross_a = Mul(a.fee, b.size), cross_b = Mul(b.fee, a.size);
        return cross_a > cross_b;
    }
 
    friend inline std::strong_ordering operator<=>(const FeeFrac& a, const FeeFrac& b) noexcept
    {
        auto cross_a = Mul(a.fee, b.size), cross_b = Mul(b.fee, a.size);
        if (cross_a == cross_b) return b.size <=> a.size;
        return cross_a <=> cross_b;
    }
 
    friend inline void swap(FeeFrac& a, FeeFrac& b) noexcept
    {
        std::swap(a.fee, b.fee);
        std::swap(a.size, b.size);
    }
};
 
std::partial_ordering CompareChunks(std::span<const FeeFrac> chunks0, std::span<const FeeFrac> chunks1);
 
template<typename Tag>
struct FeePerUnit : public FeeFrac
{
    // Inherit FeeFrac constructors.
    using FeeFrac::FeeFrac;
 
    static FeePerUnit FromFeeFrac(const FeeFrac& feefrac) noexcept
    {
        return {feefrac.fee, feefrac.size};
    }
};
 
// FeePerUnit instance for satoshi / vbyte.
struct VSizeTag {};
using FeePerVSize = FeePerUnit<VSizeTag>;
 
// FeePerUnit instance for satoshi / WU.
struct WeightTag {};
using FeePerWeight = FeePerUnit<WeightTag>;
 
#endif // BITCOIN_UTIL_FEEFRAC_H