path: root/libevmasm/GasMeter.cpp

/*
    This file is part of cpp-ethereum.

    cpp-ethereum 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.

    cpp-ethereum 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 cpp-ethereum.  If not, see <http://www.gnu.org/licenses/>.
*/
/** @file GasMeter.cpp
 * @author Christian <c@ethdev.com>
 * @date 2015
 */

#include "GasMeter.h"
#include <libevmasm/KnownState.h>
using namespace std;
using namespace dev;
using namespace dev::eth;

GasMeter::GasConsumption& GasMeter::GasConsumption::operator+=(GasConsumption const& _other)
{
    if (_other.isInfinite && !isInfinite)
        *this = infinite();
    if (isInfinite)
        return *this;
    bigint v = bigint(value) + _other.value;
    if (v > numeric_limits<u256>::max())
        *this = infinite();
    else
        value = u256(v);
    return *this;
}

GasMeter::GasConsumption GasMeter::estimateMax(AssemblyItem const& _item)
{
    GasConsumption gas;
    switch (_item.type())
    {
    case Push:
    case PushTag:
    case PushData:
    case PushString:
    case PushSub:
    case PushSubSize:
    case PushProgramSize:
    case PushLibraryAddress:
        gas = runGas(Instruction::PUSH1);
        break;
    case Tag:
        gas = runGas(Instruction::JUMPDEST);
        break;
    case Operation:
    {
        ExpressionClasses& classes = m_state->expressionClasses();
        gas = runGas(_item.instruction());
        switch (_item.instruction())
        {
        case Instruction::SSTORE:
        {
            ExpressionClasses::Id slot = m_state->relativeStackElement(0);
            ExpressionClasses::Id value = m_state->relativeStackElement(-1);
            if (classes.knownZero(value) || (
                m_state->storageContent().count(slot) &&
                classes.knownNonZero(m_state->storageContent().at(slot))
            ))
                gas += GasCosts::sstoreResetGas; //@todo take refunds into account
            else
                gas += GasCosts::sstoreSetGas;
            break;
        }
        case Instruction::SLOAD:
            gas += GasCosts::sloadGas;
            break;
        case Instruction::RETURN:
            gas += memoryGas(0, -1);
            break;
        case Instruction::MLOAD:
        case Instruction::MSTORE:
            gas += memoryGas(classes.find(Instruction::ADD, {
                m_state->relativeStackElement(0),
                classes.find(AssemblyItem(32))
            }));
            break;
        case Instruction::MSTORE8:
            gas += memoryGas(classes.find(Instruction::ADD, {
                m_state->relativeStackElement(0),
                classes.find(AssemblyItem(1))
            }));
            break;
        case Instruction::SHA3:
            gas = GasCosts::sha3Gas;
            gas += wordGas(GasCosts::sha3WordGas, m_state->relativeStackElement(-1));
            gas += memoryGas(0, -1);
            break;
        case Instruction::CALLDATACOPY:
        case Instruction::CODECOPY:
            gas += memoryGas(0, -2);
            gas += wordGas(GasCosts::copyGas, m_state->relativeStackElement(-2));
            break;
        case Instruction::EXTCODECOPY:
            gas += memoryGas(-1, -3);
            gas += wordGas(GasCosts::copyGas, m_state->relativeStackElement(-3));
            break;
        case Instruction::LOG0:
        case Instruction::LOG1:
        case Instruction::LOG2:
        case Instruction::LOG3:
        case Instruction::LOG4:
        {
            unsigned n = unsigned(_item.instruction()) - unsigned(Instruction::LOG0);
            gas = GasCosts::logGas + GasCosts::logTopicGas * n;
            gas += memoryGas(0, -1);
            if (u256 const* value = classes.knownConstant(m_state->relativeStackElement(-1)))
                gas += GasCosts::logDataGas * (*value);
            else
                gas = GasConsumption::infinite();
            break;
        }
        case Instruction::CALL:
        case Instruction::CALLCODE:
        case Instruction::DELEGATECALL:
        {
            gas = GasCosts::callGas;
            if (u256 const* value = classes.knownConstant(m_state->relativeStackElement(0)))
                gas += (*value);
            else
                gas = GasConsumption::infinite();
            if (_item.instruction() == Instruction::CALL)
                gas += GasCosts::callNewAccountGas; // We very rarely know whether the address exists.
            int valueSize = _item.instruction() == Instruction::DELEGATECALL ? 0 : 1;
            if (!classes.knownZero(m_state->relativeStackElement(-1 - valueSize)))
                gas += GasCosts::callValueTransferGas;
            gas += memoryGas(-2 - valueSize, -3 - valueSize);
            gas += memoryGas(-4 - valueSize, -5 - valueSize);
            break;
        }
        case Instruction::CREATE:
            gas = GasCosts::createGas;
            gas += memoryGas(-1, -2);
            break;
        case Instruction::EXP:
            gas = GasCosts::expGas;
            if (u256 const* value = classes.knownConstant(m_state->relativeStackElement(-1)))
                gas += GasCosts::expByteGas * (32 - (h256(*value).firstBitSet() / 8));
            else
                gas += GasCosts::expByteGas * 32;
            break;
        default:
            break;
        }
        break;
    }
    default:
        gas = GasConsumption::infinite();
        break;
    }

    m_state->feedItem(_item);
    return gas;
}

GasMeter::GasConsumption GasMeter::wordGas(u256 const& _multiplier, ExpressionClasses::Id _position)
{
    u256 const* value = m_state->expressionClasses().knownConstant(_position);
    if (!value)
        return GasConsumption::infinite();
    return GasConsumption(_multiplier * ((*value + 31) / 32));
}

GasMeter::GasConsumption GasMeter::memoryGas(ExpressionClasses::Id _position)
{
    u256 const* value = m_state->expressionClasses().knownConstant(_position);
    if (!value)
        return GasConsumption::infinite();
    if (*value < m_largestMemoryAccess)
        return GasConsumption(u256(0));
    u256 previous = m_largestMemoryAccess;
    m_largestMemoryAccess = *value;
    auto memGas = [=](u256 const& pos) -> u256
    {
        u256 size = (pos + 31) / 32;
        return GasCosts::memoryGas * size + size * size / GasCosts::quadCoeffDiv;
    };
    return memGas(*value) - memGas(previous);
}

GasMeter::GasConsumption GasMeter::memoryGas(int _stackPosOffset, int _stackPosSize)
{
    ExpressionClasses& classes = m_state->expressionClasses();
    if (classes.knownZero(m_state->relativeStackElement(_stackPosSize)))
        return GasConsumption(0);
    else
        return memoryGas(classes.find(Instruction::ADD, {
            m_state->relativeStackElement(_stackPosOffset),
            m_state->relativeStackElement(_stackPosSize)
        }));
}

unsigned GasMeter::runGas(Instruction _instruction)
{
    if (_instruction == Instruction::JUMPDEST)
        return 1;

    switch (instructionInfo(_instruction).gasPriceTier)
    {
    case 0: return GasCosts::tier0Gas;
    case 1: return GasCosts::tier1Gas;
    case 2: return GasCosts::tier2Gas;
    case 3: return GasCosts::tier3Gas;
    case 4: return GasCosts::tier4Gas;
    case 5: return GasCosts::tier5Gas;
    case 6: return GasCosts::tier6Gas;
    case 7: return GasCosts::tier7Gas;
    default: break;
    }
    assertThrow(false, OptimizerException, "Invalid gas tier.");
    return 0;
}