uint256.h

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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-present 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_UINT256_H
#define BITCOIN_UINT256_H

#include <crypto/common.h>
#include <span.h>
#include <util/strencodings.h>
#include <util/string.h>

#include <algorithm>
#include <array>
#include <cassert>
#include <cstdint>
#include <cstring>
#include <optional>
#include <string>
#include <string_view>

template<unsigned int BITS>
class base_blob
{
protected:
    static constexpr int WIDTH = BITS / 8;
    static_assert(BITS % 8 == 0, "base_blob currently only supports whole bytes.");
    std::array<uint8_t, WIDTH> m_data;
    static_assert(WIDTH == sizeof(m_data), "Sanity check");

public:
    /* construct 0 value by default */
    constexpr base_blob() : m_data() {}

    /* constructor for constants between 1 and 255 */
    constexpr explicit base_blob(uint8_t v) : m_data{v} {}

    constexpr explicit base_blob(std::span<const unsigned char> vch)
    {
        assert(vch.size() == WIDTH);
        std::copy(vch.begin(), vch.end(), m_data.begin());
    }

    consteval explicit base_blob(std::string_view hex_str);

    constexpr bool IsNull() const
    {
        return std::all_of(m_data.begin(), m_data.end(), [](uint8_t val) {
            return val == 0;
        });
    }

    constexpr void SetNull()
    {
        std::fill(m_data.begin(), m_data.end(), 0);
    }

    constexpr int Compare(const base_blob& other) const { return std::memcmp(m_data.data(), other.m_data.data(), WIDTH); }

    friend constexpr bool operator==(const base_blob& a, const base_blob& b) { return a.Compare(b) == 0; }
    friend constexpr bool operator<(const base_blob& a, const base_blob& b) { return a.Compare(b) < 0; }

    std::string GetHex() const;
    std::string ToString() const;
    constexpr const unsigned char* data() const { return m_data.data(); }
    constexpr unsigned char* data() { return m_data.data(); }

    constexpr unsigned char* begin() { return m_data.data(); }
    constexpr unsigned char* end() { return m_data.data() + WIDTH; }

    constexpr const unsigned char* begin() const { return m_data.data(); }
    constexpr const unsigned char* end() const { return m_data.data() + WIDTH; }

    static constexpr unsigned int size() { return WIDTH; }

    constexpr uint64_t GetUint64(int pos) const { return ReadLE64(m_data.data() + pos * 8); }

    template<typename Stream>
    void Serialize(Stream& s) const
    {
        s << std::span(m_data);
    }

    template<typename Stream>
    void Unserialize(Stream& s)
    {
        s.read(MakeWritableByteSpan(m_data));
    }
};

template <unsigned int BITS>
consteval base_blob<BITS>::base_blob(std::string_view hex_str)
{
    if (hex_str.length() != m_data.size() * 2) throw "Hex string must fit exactly";
    auto str_it = hex_str.rbegin();
    for (auto& elem : m_data) {
        auto lo = util::ConstevalHexDigit(*(str_it++));
        elem = (util::ConstevalHexDigit(*(str_it++)) << 4) | lo;
    }
}

namespace detail {
template <class uintN_t>
std::optional<uintN_t> FromHex(std::string_view str)
{
    if (uintN_t::size() * 2 != str.size() || !IsHex(str)) return std::nullopt;
    uintN_t rv;
    unsigned char* p1 = rv.begin();
    unsigned char* pend = rv.end();
    size_t digits = str.size();
    while (digits > 0 && p1 < pend) {
        *p1 = ::HexDigit(str[--digits]);
        if (digits > 0) {
            *p1 |= ((unsigned char)::HexDigit(str[--digits]) << 4);
            p1++;
        }
    }
    return rv;
}
template <class uintN_t>
std::optional<uintN_t> FromUserHex(std::string_view input)
{
    input = util::RemovePrefixView(input, "0x");
    constexpr auto expected_size{uintN_t::size() * 2};
    if (input.size() < expected_size) {
        auto padded = std::string(expected_size, '0');
        std::copy(input.begin(), input.end(), padded.begin() + expected_size - input.size());
        return FromHex<uintN_t>(padded);
    }
    return FromHex<uintN_t>(input);
}
} // namespace detail

class uint160 : public base_blob<160> {
public:
    static std::optional<uint160> FromHex(std::string_view str) { return detail::FromHex<uint160>(str); }
    constexpr uint160() = default;
    constexpr explicit uint160(std::span<const unsigned char> vch) : base_blob<160>(vch) {}
};

class uint256 : public base_blob<256> {
public:
    static std::optional<uint256> FromHex(std::string_view str) { return detail::FromHex<uint256>(str); }
    static std::optional<uint256> FromUserHex(std::string_view str) { return detail::FromUserHex<uint256>(str); }
    constexpr uint256() = default;
    consteval explicit uint256(std::string_view hex_str) : base_blob<256>(hex_str) {}
    constexpr explicit uint256(uint8_t v) : base_blob<256>(v) {}
    constexpr explicit uint256(std::span<const unsigned char> vch) : base_blob<256>(vch) {}
    static const uint256 ZERO;
    static const uint256 ONE;
};

#endif // BITCOIN_UINT256_H