/src/solidity/libsolutil/Numeric.h

Source
/*
  This file is part of solidity.

  solidity is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  solidity is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with solidity.  If not, see <http://www.gnu.org/licenses/>.
*/
// SPDX-License-Identifier: GPL-3.0
/**
 * Definition of u256 and similar types and helper functions.
 */

#pragma once

#include <libsolutil/Common.h>
#include <libsolutil/CommonData.h>

#include <boost/version.hpp>

// TODO: do this only conditionally as soon as a boost version with gcc 12 support is released.
#if defined(__GNUC__) && !defined(__clang__) && (__GNUC__ >= 12)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
#pragma GCC diagnostic ignored "-Warray-bounds"
#pragma GCC diagnostic ignored "-Wstringop-overread"
#pragma GCC diagnostic ignored "-Waggressive-loop-optimizations"
#endif
#include <boost/multiprecision/cpp_int.hpp>
#if defined(__GNUC__) && !defined(__clang__) && (__GNUC__ >= 12)
#pragma GCC diagnostic pop
#endif

#include <limits>

namespace solidity
{

// Numeric types.
using bigint = boost::multiprecision::cpp_int;
using u256 = boost::multiprecision::uint256_t;
using s256 = boost::multiprecision::int256_t;
using u512 = boost::multiprecision::uint512_t;


/// Interprets @a _u as a two's complement signed number and returns the resulting s256.
inline s256 u2s(u256 _u)
{
  static bigint const c_end = bigint(1) << 256;
  if (boost::multiprecision::bit_test(_u, 255))
    return s256(-(c_end - _u));
  else
    return s256(_u);
}

/// @returns the two's complement signed representation of the signed number _u.
inline u256 s2u(s256 _u)
{
  static bigint const c_end = bigint(1) << 256;
  if (_u >= 0)
    return u256(_u);
  else
    return u256(c_end + _u);
}

inline u256 exp256(u256 _base, u256 _exponent)
{
  using boost::multiprecision::limb_type;
  u256 result = 1;
  while (_exponent)
  {
    if (boost::multiprecision::bit_test(_exponent, 0))
      result *= _base;
    _base *= _base;
    _exponent >>= 1;
  }
  return result;
}

/// Checks whether _mantissa * (X ** _exp) fits into 4096 bits,
/// where X is given indirectly via _log2OfBase = log2(X).
bool fitsPrecisionBaseX(bigint const& _mantissa, double _log2OfBase, uint32_t _exp);


// Big-endian to/from host endian conversion functions.

/// Converts a templated integer value to the big-endian byte-stream represented on a templated collection.
/// The size of the collection object will be unchanged. If it is too small, it will not represent the
/// value properly, if too big then the additional elements will be zeroed out.
/// @a Out will typically be either std::string or bytes.
/// @a T will typically by unsigned, u160, u256 or bigint.
template <class T, class Out>
inline void toBigEndian(T _val, Out&& o_out)
{
  static_assert(std::is_same<bigint, T>::value || !std::numeric_limits<T>::is_signed, "only unsigned types or bigint supported"); //bigint does not carry sign bit on shift
  for (auto i = o_out.size(); i != 0u; _val >>= 8u, i--)
  {
    T v = _val & (T)0xffu;
    o_out[i - 1u] = (typename std::remove_reference_t<Out>::value_type)(uint8_t)v;
  }
}

/// Converts a big-endian byte-stream represented on a templated collection to a templated integer value.
/// @a In will typically be either std::string or bytes.
/// @a T will typically by unsigned, u256 or bigint.
template <class T, class In>
inline T fromBigEndian(In const& _bytes)
{
  T ret = (T)0;
  for (auto i: _bytes)
    ret = (T)((ret << 8) | (uint8_t)(typename std::make_unsigned<typename In::value_type>::type)i);
  return ret;
}
inline bytes toBigEndian(u256 _val) { bytes ret(32); toBigEndian(_val, ret); return ret; }

/// Convenience function for toBigEndian.
/// @returns a byte array just big enough to represent @a _val.
template <class T>
inline bytes toCompactBigEndian(T _val, unsigned _min = 0)
{
  static_assert(std::is_same<bigint, T>::value || !std::numeric_limits<T>::is_signed, "only unsigned types or bigint supported"); //bigint does not carry sign bit on shift
  unsigned i = 0;
  for (T v = _val; v; ++i, v >>= 8) {}
  bytes ret(std::max<unsigned>(_min, i), 0);
  toBigEndian(_val, ret);
  return ret;
}

/// Convenience function for conversion of a u256 to hex
inline std::string toHex(u256 val)
{
  return util::toHex(toBigEndian(val));
}

template <class T>
inline std::string toCompactHexWithPrefix(T _value)
{
  return "0x" + util::toHex(toCompactBigEndian(_value, 1));
}

/// Returns decimal representation for small numbers and hex for large numbers.
inline std::string formatNumber(bigint const& _value)
{
  if (_value < 0)
    return "-" + formatNumber(-_value);
  if (_value > 0x1000000)
    return "0x" + util::toHex(toCompactBigEndian(_value, 1));
  else
    return _value.str();
}

inline std::string formatNumber(u256 const& _value)
{
  if (_value > 0x1000000)
    return toCompactHexWithPrefix(_value);
  else
    return _value.str();
}


// Algorithms for string and string-like collections.

/// Determine bytes required to encode the given integer value. @returns 0 if @a _i is zero.
template <class T>
inline unsigned numberEncodingSize(T _i)
{
  static_assert(std::is_same<bigint, T>::value || !std::numeric_limits<T>::is_signed, "only unsigned types or bigint supported"); //bigint does not carry sign bit on shift
  unsigned i = 0;
  for (; _i != 0; ++i, _i >>= 8) {}
  return i;
}

}

Coverage Report

Created: 2026-07-13 07:08