b58_utils.h

//------------------------------------------------------------------------------
/*
    This file is part of rippled: https://github.com/ripple/rippled
    Copyright (c) 2022 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_PROTOCOL_B58_UTILS_H_INCLUDED
#define RIPPLE_PROTOCOL_B58_UTILS_H_INCLUDED
 
#include <ripple/basics/contract.h>
 
#include <boost/outcome.hpp>
#include <boost/outcome/result.hpp>
 
#include <cassert>
#include <cinttypes>
#include <span>
#include <system_error>
#include <tuple>
 
namespace ripple {
 
template <class T>
using Result = boost::outcome_v2::result<T, std::error_code>;
 
#ifndef _MSC_VER
namespace b58_fast {
namespace detail {
 
// This optimizes to what hand written asm would do (single divide)
[[nodiscard]] inline std::tuple<std::uint64_t, std::uint64_t>
div_rem(std::uint64_t a, std::uint64_t b)
{
    return {a / b, a % b};
}
 
// This optimizes to what hand written asm would do (single multiply)
[[nodiscard]] inline std::tuple<std::uint64_t, std::uint64_t>
carrying_mul(std::uint64_t a, std::uint64_t b, std::uint64_t carry)
{
    unsigned __int128 const x = a;
    unsigned __int128 const y = b;
    unsigned __int128 const c = x * y + carry;
    return {c & 0xffff'ffff'ffff'ffff, c >> 64};
}
 
[[nodiscard]] inline std::tuple<std::uint64_t, std::uint64_t>
carrying_add(std::uint64_t a, std::uint64_t b)
{
    unsigned __int128 const x = a;
    unsigned __int128 const y = b;
    unsigned __int128 const c = x + y;
    return {c & 0xffff'ffff'ffff'ffff, c >> 64};
}
 
// Add a u64 to a "big uint" value inplace.
// The bigint value is stored with the smallest coefficients first
// (i.e a[0] is the 2^0 coefficient, a[n] is the 2^(64*n) coefficient)
// panics if overflows (this is a specialized adder for b58 decoding.
// it should never overflow).
inline void
inplace_bigint_add(std::span<std::uint64_t> a, std::uint64_t b)
{
    if (a.size() <= 1)
    {
        ripple::LogicError("Input span too small for inplace_bigint_add");
    }
 
    std::uint64_t carry;
    std::tie(a[0], carry) = carrying_add(a[0], b);
 
    for (auto& v : a.subspan(1))
    {
        if (!carry)
        {
            return;
        }
        std::tie(v, carry) = carrying_add(v, 1);
    }
    if (carry)
    {
        LogicError("Overflow in inplace_bigint_add");
    }
}
 
inline void
inplace_bigint_mul(std::span<std::uint64_t> a, std::uint64_t b)
{
    if (a.empty())
    {
        LogicError("Empty span passed to inplace_bigint_mul");
    }
 
    auto const last_index = a.size() - 1;
    if (a[last_index] != 0)
    {
        LogicError("Non-zero element in inplace_bigint_mul last index");
    }
 
    std::uint64_t carry = 0;
    for (auto& coeff : a.subspan(0, last_index))
    {
        std::tie(coeff, carry) = carrying_mul(coeff, b, carry);
    }
    a[last_index] = carry;
}
// divide a "big uint" value inplace and return the mod
// numerator is stored so smallest coefficients come first
[[nodiscard]] inline std::uint64_t
inplace_bigint_div_rem(std::span<uint64_t> numerator, std::uint64_t divisor)
{
    if (numerator.size() == 0)
    {
        // should never happen, but if it does then it seems natural to define
        // the a null set of numbers to be zero, so the remainder is also zero.
        assert(0);
        return 0;
    }
 
    auto to_u128 = [](std::uint64_t high,
                      std::uint64_t low) -> unsigned __int128 {
        unsigned __int128 const high128 = high;
        unsigned __int128 const low128 = low;
        return ((high128 << 64) | low128);
    };
    auto div_rem_64 =
        [](unsigned __int128 num,
           std::uint64_t denom) -> std::tuple<std::uint64_t, std::uint64_t> {
        unsigned __int128 const denom128 = denom;
        unsigned __int128 const d = num / denom128;
        unsigned __int128 const r = num - (denom128 * d);
        assert(d >> 64 == 0);
        assert(r >> 64 == 0);
        return {static_cast<std::uint64_t>(d), static_cast<std::uint64_t>(r)};
    };
 
    std::uint64_t prev_rem = 0;
    int const last_index = numerator.size() - 1;
    std::tie(numerator[last_index], prev_rem) =
        div_rem(numerator[last_index], divisor);
    for (int i = last_index - 1; i >= 0; --i)
    {
        unsigned __int128 const cur_num = to_u128(prev_rem, numerator[i]);
        std::tie(numerator[i], prev_rem) = div_rem_64(cur_num, divisor);
    }
    return prev_rem;
}
 
// convert from base 58^10 to base 58
// put largest coeffs first
// the `_be` suffix stands for "big endian"
[[nodiscard]] inline std::array<std::uint8_t, 10>
b58_10_to_b58_be(std::uint64_t input)
{
    constexpr std::uint64_t B_58_10 = 430804206899405824;  // 58^10;
    if (input >= B_58_10)
    {
        LogicError("Input to b58_10_to_b58_be equals or exceeds 58^10.");
    }
 
    constexpr std::size_t resultSize = 10;
    std::array<std::uint8_t, resultSize> result{};
    int i = 0;
    while (input > 0)
    {
        std::uint64_t rem;
        std::tie(input, rem) = div_rem(input, 58);
        result[resultSize - 1 - i] = rem;
        i += 1;
    }
 
    return result;
}
}  // namespace detail
}  // namespace b58_fast
#endif
 
}  // namespace ripple
#endif  // RIPPLE_PROTOCOL_B58_UTILS_H_INCLUDED