path: root/libsolidity/codegen/ArrayUtils.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/>.
*/
/**
 * @author Christian <c@ethdev.com>
 * @date 2015
 * Code generation utils that handle arrays.
 */

#include <libsolidity/codegen/ArrayUtils.h>
#include <libevmcore/Instruction.h>
#include <libsolidity/codegen/CompilerContext.h>
#include <libsolidity/codegen/CompilerUtils.h>
#include <libsolidity/ast/Types.h>
#include <libsolidity/interface/Utils.h>
#include <libsolidity/codegen/LValue.h>

using namespace std;
using namespace dev;
using namespace solidity;

void ArrayUtils::copyArrayToStorage(ArrayType const& _targetType, ArrayType const& _sourceType) const
{
    // this copies source to target and also clears target if it was larger
    // need to leave "target_ref target_byte_off" on the stack at the end

    // stack layout: [source_ref] [source length] target_ref (top)
    solAssert(_targetType.location() == DataLocation::Storage, "");

    IntegerType uint256(256);
    Type const* targetBaseType = _targetType.isByteArray() ? &uint256 : &(*_targetType.baseType());
    Type const* sourceBaseType = _sourceType.isByteArray() ? &uint256 : &(*_sourceType.baseType());

    // TODO unroll loop for small sizes

    bool sourceIsStorage = _sourceType.location() == DataLocation::Storage;
    bool fromCalldata = _sourceType.location() == DataLocation::CallData;
    bool directCopy = sourceIsStorage && sourceBaseType->isValueType() && *sourceBaseType == *targetBaseType;
    bool haveByteOffsetSource = !directCopy && sourceIsStorage && sourceBaseType->storageBytes() <= 16;
    bool haveByteOffsetTarget = !directCopy && targetBaseType->storageBytes() <= 16;
    unsigned byteOffsetSize = (haveByteOffsetSource ? 1 : 0) + (haveByteOffsetTarget ? 1 : 0);

    // stack: source_ref [source_length] target_ref
    // store target_ref
    for (unsigned i = _sourceType.sizeOnStack(); i > 0; --i)
        m_context << eth::swapInstruction(i);
    // stack: target_ref source_ref [source_length]
    // stack: target_ref source_ref [source_length]
    // retrieve source length
    if (_sourceType.location() != DataLocation::CallData || !_sourceType.isDynamicallySized())
        retrieveLength(_sourceType); // otherwise, length is already there
    if (_sourceType.location() == DataLocation::Memory && _sourceType.isDynamicallySized())
    {
        // increment source pointer to point to data
        m_context << eth::Instruction::SWAP1 << u256(0x20);
        m_context << eth::Instruction::ADD << eth::Instruction::SWAP1;
    }

    // stack: target_ref source_ref source_length
    m_context << eth::Instruction::DUP3;
    // stack: target_ref source_ref source_length target_ref
    retrieveLength(_targetType);
    // stack: target_ref source_ref source_length target_ref target_length
    if (_targetType.isDynamicallySized())
        // store new target length
        if (!_targetType.isByteArray())
            // Otherwise, length will be stored below.
            m_context << eth::Instruction::DUP3 << eth::Instruction::DUP3 << eth::Instruction::SSTORE;
    if (sourceBaseType->category() == Type::Category::Mapping)
    {
        solAssert(targetBaseType->category() == Type::Category::Mapping, "");
        solAssert(_sourceType.location() == DataLocation::Storage, "");
        // nothing to copy
        m_context
            << eth::Instruction::POP << eth::Instruction::POP
            << eth::Instruction::POP << eth::Instruction::POP;
        return;
    }
    // stack: target_ref source_ref source_length target_ref target_length
    // compute hashes (data positions)
    m_context << eth::Instruction::SWAP1;
    if (_targetType.isDynamicallySized())
        CompilerUtils(m_context).computeHashStatic();
    // stack: target_ref source_ref source_length target_length target_data_pos
    m_context << eth::Instruction::SWAP1;
    convertLengthToSize(_targetType);
    m_context << eth::Instruction::DUP2 << eth::Instruction::ADD;
    // stack: target_ref source_ref source_length target_data_pos target_data_end
    m_context << eth::Instruction::SWAP3;
    // stack: target_ref target_data_end source_length target_data_pos source_ref

    eth::AssemblyItem copyLoopEndWithoutByteOffset = m_context.newTag();

    // special case for short byte arrays: Store them together with their length.
    if (_targetType.isByteArray())
    {
        // stack: target_ref target_data_end source_length target_data_pos source_ref
        m_context << eth::Instruction::DUP3 << u256(31) << eth::Instruction::LT;
        eth::AssemblyItem longByteArray = m_context.appendConditionalJump();
        // store the short byte array
        solAssert(_sourceType.isByteArray(), "");
        if (_sourceType.location() == DataLocation::Storage)
        {
            // just copy the slot, it contains length and data
            m_context << eth::Instruction::DUP1 << eth::Instruction::SLOAD;
            m_context << eth::Instruction::DUP6 << eth::Instruction::SSTORE;
        }
        else
        {
            m_context << eth::Instruction::DUP1;
            CompilerUtils(m_context).loadFromMemoryDynamic(*sourceBaseType, fromCalldata, true, false);
            // stack: target_ref target_data_end source_length target_data_pos source_ref value
            // clear the lower-order byte - which will hold the length
            m_context << u256(0xff) << eth::Instruction::NOT << eth::Instruction::AND;
            // fetch the length and shift it left by one
            m_context << eth::Instruction::DUP4 << eth::Instruction::DUP1 << eth::Instruction::ADD;
            // combine value and length and store them
            m_context << eth::Instruction::OR << eth::Instruction::DUP6 << eth::Instruction::SSTORE;
        }
        // end of special case, jump right into cleaning target data area
        m_context.appendJumpTo(copyLoopEndWithoutByteOffset);
        m_context << longByteArray;
        // Store length (2*length+1)
        m_context << eth::Instruction::DUP3 << eth::Instruction::DUP1 << eth::Instruction::ADD;
        m_context << u256(1) << eth::Instruction::ADD;
        m_context << eth::Instruction::DUP6 << eth::Instruction::SSTORE;
    }

    // skip copying if source length is zero
    m_context << eth::Instruction::DUP3 << eth::Instruction::ISZERO;
    m_context.appendConditionalJumpTo(copyLoopEndWithoutByteOffset);

    if (_sourceType.location() == DataLocation::Storage && _sourceType.isDynamicallySized())
        CompilerUtils(m_context).computeHashStatic();
    // stack: target_ref target_data_end source_length target_data_pos source_data_pos
    m_context << eth::Instruction::SWAP2;
    convertLengthToSize(_sourceType);
    m_context << eth::Instruction::DUP3 << eth::Instruction::ADD;
    // stack: target_ref target_data_end source_data_pos target_data_pos source_data_end
    if (haveByteOffsetTarget)
        m_context << u256(0);
    if (haveByteOffsetSource)
        m_context << u256(0);
    // stack: target_ref target_data_end source_data_pos target_data_pos source_data_end [target_byte_offset] [source_byte_offset]
    eth::AssemblyItem copyLoopStart = m_context.newTag();
    m_context << copyLoopStart;
    // check for loop condition
    m_context
        << eth::dupInstruction(3 + byteOffsetSize) << eth::dupInstruction(2 + byteOffsetSize)
        << eth::Instruction::GT << eth::Instruction::ISZERO;
    eth::AssemblyItem copyLoopEnd = m_context.appendConditionalJump();
    // stack: target_ref target_data_end source_data_pos target_data_pos source_data_end [target_byte_offset] [source_byte_offset]
    // copy
    if (sourceBaseType->category() == Type::Category::Array)
    {
        solAssert(byteOffsetSize == 0, "Byte offset for array as base type.");
        auto const& sourceBaseArrayType = dynamic_cast<ArrayType const&>(*sourceBaseType);
        m_context << eth::Instruction::DUP3;
        if (sourceBaseArrayType.location() == DataLocation::Memory)
            m_context << eth::Instruction::MLOAD;
        m_context << eth::Instruction::DUP3;
        copyArrayToStorage(dynamic_cast<ArrayType const&>(*targetBaseType), sourceBaseArrayType);
        m_context << eth::Instruction::POP;
    }
    else if (directCopy)
    {
        solAssert(byteOffsetSize == 0, "Byte offset for direct copy.");
        m_context
            << eth::Instruction::DUP3 << eth::Instruction::SLOAD
            << eth::Instruction::DUP3 << eth::Instruction::SSTORE;
    }
    else
    {
        // Note that we have to copy each element on its own in case conversion is involved.
        // We might copy too much if there is padding at the last element, but this way end
        // checking is easier.
        // stack: target_ref target_data_end source_data_pos target_data_pos source_data_end [target_byte_offset] [source_byte_offset]
        m_context << eth::dupInstruction(3 + byteOffsetSize);
        if (_sourceType.location() == DataLocation::Storage)
        {
            if (haveByteOffsetSource)
                m_context << eth::Instruction::DUP2;
            else
                m_context << u256(0);
            StorageItem(m_context, *sourceBaseType).retrieveValue(SourceLocation(), true);
        }
        else if (sourceBaseType->isValueType())
            CompilerUtils(m_context).loadFromMemoryDynamic(*sourceBaseType, fromCalldata, true, false);
        else
            solAssert(false, "Copying of type " + _sourceType.toString(false) + " to storage not yet supported.");
        // stack: target_ref target_data_end source_data_pos target_data_pos source_data_end [target_byte_offset] [source_byte_offset] <source_value>...
        solAssert(
            2 + byteOffsetSize + sourceBaseType->sizeOnStack() <= 16,
            "Stack too deep, try removing local variables."
        );
        // fetch target storage reference
        m_context << eth::dupInstruction(2 + byteOffsetSize + sourceBaseType->sizeOnStack());
        if (haveByteOffsetTarget)
            m_context << eth::dupInstruction(1 + byteOffsetSize + sourceBaseType->sizeOnStack());
        else
            m_context << u256(0);
        StorageItem(m_context, *targetBaseType).storeValue(*sourceBaseType, SourceLocation(), true);
    }
    // stack: target_ref target_data_end source_data_pos target_data_pos source_data_end [target_byte_offset] [source_byte_offset]
    // increment source
    if (haveByteOffsetSource)
        incrementByteOffset(sourceBaseType->storageBytes(), 1, haveByteOffsetTarget ? 5 : 4);
    else
    {
        m_context << eth::swapInstruction(2 + byteOffsetSize);
        if (sourceIsStorage)
            m_context << sourceBaseType->storageSize();
        else if (_sourceType.location() == DataLocation::Memory)
            m_context << sourceBaseType->memoryHeadSize();
        else
            m_context << sourceBaseType->calldataEncodedSize(true);
        m_context
            << eth::Instruction::ADD
            << eth::swapInstruction(2 + byteOffsetSize);
    }
    // increment target
    if (haveByteOffsetTarget)
        incrementByteOffset(targetBaseType->storageBytes(), byteOffsetSize, byteOffsetSize + 2);
    else
        m_context
            << eth::swapInstruction(1 + byteOffsetSize)
            << targetBaseType->storageSize()
            << eth::Instruction::ADD
            << eth::swapInstruction(1 + byteOffsetSize);
    m_context.appendJumpTo(copyLoopStart);
    m_context << copyLoopEnd;
    if (haveByteOffsetTarget)
    {
        // clear elements that might be left over in the current slot in target
        // stack: target_ref target_data_end source_data_pos target_data_pos source_data_end target_byte_offset [source_byte_offset]
        m_context << eth::dupInstruction(byteOffsetSize) << eth::Instruction::ISZERO;
        eth::AssemblyItem copyCleanupLoopEnd = m_context.appendConditionalJump();
        m_context << eth::dupInstruction(2 + byteOffsetSize) << eth::dupInstruction(1 + byteOffsetSize);
        StorageItem(m_context, *targetBaseType).setToZero(SourceLocation(), true);
        incrementByteOffset(targetBaseType->storageBytes(), byteOffsetSize, byteOffsetSize + 2);
        m_context.appendJumpTo(copyLoopEnd);

        m_context << copyCleanupLoopEnd;
        m_context << eth::Instruction::POP; // might pop the source, but then target is popped next
    }
    if (haveByteOffsetSource)
        m_context << eth::Instruction::POP;
    m_context << copyLoopEndWithoutByteOffset;

    // zero-out leftovers in target
    // stack: target_ref target_data_end source_data_pos target_data_pos_updated source_data_end
    m_context << eth::Instruction::POP << eth::Instruction::SWAP1 << eth::Instruction::POP;
    // stack: target_ref target_data_end target_data_pos_updated
    clearStorageLoop(*targetBaseType);
    m_context << eth::Instruction::POP;
}

void ArrayUtils::copyArrayToMemory(ArrayType const& _sourceType, bool _padToWordBoundaries) const
{
    solAssert(
        !_sourceType.baseType()->isDynamicallySized(),
        "Nested dynamic arrays not implemented here."
    );
    CompilerUtils utils(m_context);
    unsigned baseSize = 1;
    if (!_sourceType.isByteArray())
        // We always pad the elements, regardless of _padToWordBoundaries.
        baseSize = _sourceType.baseType()->calldataEncodedSize();

    if (_sourceType.location() == DataLocation::CallData)
    {
        if (!_sourceType.isDynamicallySized())
            m_context << _sourceType.length();
        if (baseSize > 1)
            m_context << u256(baseSize) << eth::Instruction::MUL;
        // stack: target source_offset source_len
        m_context << eth::Instruction::DUP1 << eth::Instruction::DUP3 << eth::Instruction::DUP5;
        // stack: target source_offset source_len source_len source_offset target
        m_context << eth::Instruction::CALLDATACOPY;
        m_context << eth::Instruction::DUP3 << eth::Instruction::ADD;
        m_context << eth::Instruction::SWAP2 << eth::Instruction::POP << eth::Instruction::POP;
    }
    else if (_sourceType.location() == DataLocation::Memory)
    {
        retrieveLength(_sourceType);
        // stack: target source length
        if (!_sourceType.baseType()->isValueType())
        {
            // copy using a loop
            m_context << u256(0) << eth::Instruction::SWAP3;
            // stack: counter source length target
            auto repeat = m_context.newTag();
            m_context << repeat;
            m_context << eth::Instruction::DUP2 << eth::Instruction::DUP5;
            m_context << eth::Instruction::LT << eth::Instruction::ISZERO;
            auto loopEnd = m_context.appendConditionalJump();
            m_context << eth::Instruction::DUP3 << eth::Instruction::DUP5;
            accessIndex(_sourceType, false);
            MemoryItem(m_context, *_sourceType.baseType(), true).retrieveValue(SourceLocation(), true);
            if (auto baseArray = dynamic_cast<ArrayType const*>(_sourceType.baseType().get()))
                copyArrayToMemory(*baseArray, _padToWordBoundaries);
            else
                utils.storeInMemoryDynamic(*_sourceType.baseType());
            m_context << eth::Instruction::SWAP3 << u256(1) << eth::Instruction::ADD;
            m_context << eth::Instruction::SWAP3;
            m_context.appendJumpTo(repeat);
            m_context << loopEnd;
            m_context << eth::Instruction::SWAP3;
            utils.popStackSlots(3);
            // stack: updated_target_pos
            return;
        }

        // memcpy using the built-in contract
        if (_sourceType.isDynamicallySized())
        {
            // change pointer to data part
            m_context << eth::Instruction::SWAP1 << u256(32) << eth::Instruction::ADD;
            m_context << eth::Instruction::SWAP1;
        }
        // convert length to size
        if (baseSize > 1)
            m_context << u256(baseSize) << eth::Instruction::MUL;
        // stack: <target> <source> <size>
        //@TODO do not use ::CALL if less than 32 bytes?
        m_context << eth::Instruction::DUP1 << eth::Instruction::DUP4 << eth::Instruction::DUP4;
        utils.memoryCopy();

        m_context << eth::Instruction::SWAP1 << eth::Instruction::POP;
        // stack: <target> <size>

        bool paddingNeeded = false;
        if (_sourceType.isDynamicallySized())
            paddingNeeded = _padToWordBoundaries && ((baseSize % 32) != 0);
        else
            paddingNeeded = _padToWordBoundaries && (((_sourceType.length() * baseSize) % 32) != 0);
        if (paddingNeeded)
        {
            // stack: <target> <size>
            m_context << eth::Instruction::SWAP1 << eth::Instruction::DUP2 << eth::Instruction::ADD;
            // stack: <length> <target + size>
            m_context << eth::Instruction::SWAP1 << u256(31) << eth::Instruction::AND;
            // stack: <target + size> <remainder = size % 32>
            eth::AssemblyItem skip = m_context.newTag();
            if (_sourceType.isDynamicallySized())
            {
                m_context << eth::Instruction::DUP1 << eth::Instruction::ISZERO;
                m_context.appendConditionalJumpTo(skip);
            }
            // round off, load from there.
            // stack <target + size> <remainder = size % 32>
            m_context << eth::Instruction::DUP1 << eth::Instruction::DUP3;
            m_context << eth::Instruction::SUB;
            // stack: target+size remainder <target + size - remainder>
            m_context << eth::Instruction::DUP1 << eth::Instruction::MLOAD;
            // Now we AND it with ~(2**(8 * (32 - remainder)) - 1)
            m_context << u256(1);
            m_context << eth::Instruction::DUP4 << u256(32) << eth::Instruction::SUB;
            // stack: ...<v> 1 <32 - remainder>
            m_context << u256(0x100) << eth::Instruction::EXP << eth::Instruction::SUB;
            m_context << eth::Instruction::NOT << eth::Instruction::AND;
            // stack: target+size remainder target+size-remainder <v & ...>
            m_context << eth::Instruction::DUP2 << eth::Instruction::MSTORE;
            // stack: target+size remainder target+size-remainder
            m_context << u256(32) << eth::Instruction::ADD;
            // stack: target+size remainder <new_padded_end>
            m_context << eth::Instruction::SWAP2 << eth::Instruction::POP;

            if (_sourceType.isDynamicallySized())
                m_context << skip.tag();
            // stack <target + "size"> <remainder = size % 32>
            m_context << eth::Instruction::POP;
        }
        else
            // stack: <target> <size>
            m_context << eth::Instruction::ADD;
    }
    else
    {
        solAssert(_sourceType.location() == DataLocation::Storage, "");
        unsigned storageBytes = _sourceType.baseType()->storageBytes();
        u256 storageSize = _sourceType.baseType()->storageSize();
        solAssert(storageSize > 1 || (storageSize == 1 && storageBytes > 0), "");

        retrieveLength(_sourceType);
        // stack here: memory_offset storage_offset length
        // jump to end if length is zero
        m_context << eth::Instruction::DUP1 << eth::Instruction::ISZERO;
        eth::AssemblyItem loopEnd = m_context.appendConditionalJump();
        // Special case for tightly-stored byte arrays
        if (_sourceType.isByteArray())
        {
            // stack here: memory_offset storage_offset length
            m_context << eth::Instruction::DUP1 << u256(31) << eth::Instruction::LT;
            eth::AssemblyItem longByteArray = m_context.appendConditionalJump();
            // store the short byte array (discard lower-order byte)
            m_context << u256(0x100) << eth::Instruction::DUP1;
            m_context << eth::Instruction::DUP4 << eth::Instruction::SLOAD;
            m_context << eth::Instruction::DIV << eth::Instruction::MUL;
            m_context << eth::Instruction::DUP4 << eth::Instruction::MSTORE;
            // stack here: memory_offset storage_offset length
            // add 32 or length to memory offset
            m_context << eth::Instruction::SWAP2;
            if (_padToWordBoundaries)
                m_context << u256(32);
            else
                m_context << eth::Instruction::DUP3;
            m_context << eth::Instruction::ADD;
            m_context << eth::Instruction::SWAP2;
            m_context.appendJumpTo(loopEnd);
            m_context << longByteArray;
        }
        // compute memory end offset
        if (baseSize > 1)
            // convert length to memory size
            m_context << u256(baseSize) << eth::Instruction::MUL;
        m_context << eth::Instruction::DUP3 << eth::Instruction::ADD << eth::Instruction::SWAP2;
        if (_sourceType.isDynamicallySized())
        {
            // actual array data is stored at SHA3(storage_offset)
            m_context << eth::Instruction::SWAP1;
            utils.computeHashStatic();
            m_context << eth::Instruction::SWAP1;
        }

        // stack here: memory_end_offset storage_data_offset memory_offset
        bool haveByteOffset = !_sourceType.isByteArray() && storageBytes <= 16;
        if (haveByteOffset)
            m_context << u256(0) << eth::Instruction::SWAP1;
        // stack here: memory_end_offset storage_data_offset [storage_byte_offset] memory_offset
        eth::AssemblyItem loopStart = m_context.newTag();
        m_context << loopStart;
        // load and store
        if (_sourceType.isByteArray())
        {
            // Packed both in storage and memory.
            m_context << eth::Instruction::DUP2 << eth::Instruction::SLOAD;
            m_context << eth::Instruction::DUP2 << eth::Instruction::MSTORE;
            // increment storage_data_offset by 1
            m_context << eth::Instruction::SWAP1 << u256(1) << eth::Instruction::ADD;
            // increment memory offset by 32
            m_context << eth::Instruction::SWAP1 << u256(32) << eth::Instruction::ADD;
        }
        else
        {
            // stack here: memory_end_offset storage_data_offset [storage_byte_offset] memory_offset
            if (haveByteOffset)
                m_context << eth::Instruction::DUP3 << eth::Instruction::DUP3;
            else
                m_context << eth::Instruction::DUP2 << u256(0);
            StorageItem(m_context, *_sourceType.baseType()).retrieveValue(SourceLocation(), true);
            if (auto baseArray = dynamic_cast<ArrayType const*>(_sourceType.baseType().get()))
                copyArrayToMemory(*baseArray, _padToWordBoundaries);
            else
                utils.storeInMemoryDynamic(*_sourceType.baseType());
            // increment storage_data_offset and byte offset
            if (haveByteOffset)
                incrementByteOffset(storageBytes, 2, 3);
            else
            {
                m_context << eth::Instruction::SWAP1;
                m_context << storageSize << eth::Instruction::ADD;
                m_context << eth::Instruction::SWAP1;
            }
        }
        // check for loop condition
        m_context << eth::Instruction::DUP1 << eth::dupInstruction(haveByteOffset ? 5 : 4);
        m_context << eth::Instruction::GT;
        m_context.appendConditionalJumpTo(loopStart);
        // stack here: memory_end_offset storage_data_offset [storage_byte_offset] memory_offset
        if (haveByteOffset)
            m_context << eth::Instruction::SWAP1 << eth::Instruction::POP;
        if (_padToWordBoundaries && baseSize % 32 != 0)
        {
            // memory_end_offset - start is the actual length (we want to compute the ceil of).
            // memory_offset - start is its next multiple of 32, but it might be off by 32.
            // so we compute: memory_end_offset += (memory_offset - memory_end_offest) & 31
            m_context << eth::Instruction::DUP3 << eth::Instruction::SWAP1 << eth::Instruction::SUB;
            m_context << u256(31) << eth::Instruction::AND;
            m_context << eth::Instruction::DUP3 << eth::Instruction::ADD;
            m_context << eth::Instruction::SWAP2;
        }
        m_context << loopEnd << eth::Instruction::POP << eth::Instruction::POP;
    }
}

void ArrayUtils::clearArray(ArrayType const& _type) const
{
    unsigned stackHeightStart = m_context.stackHeight();
    solAssert(_type.location() == DataLocation::Storage, "");
    if (_type.baseType()->storageBytes() < 32)
    {
        solAssert(_type.baseType()->isValueType(), "Invalid storage size for non-value type.");
        solAssert(_type.baseType()->storageSize() <= 1, "Invalid storage size for type.");
    }
    if (_type.baseType()->isValueType())
        solAssert(_type.baseType()->storageSize() <= 1, "Invalid size for value type.");

    m_context << eth::Instruction::POP; // remove byte offset
    if (_type.isDynamicallySized())
        clearDynamicArray(_type);
    else if (_type.length() == 0 || _type.baseType()->category() == Type::Category::Mapping)
        m_context << eth::Instruction::POP;
    else if (_type.baseType()->isValueType() && _type.storageSize() <= 5)
    {
        // unroll loop for small arrays @todo choose a good value
        // Note that we loop over storage slots here, not elements.
        for (unsigned i = 1; i < _type.storageSize(); ++i)
            m_context
                << u256(0) << eth::Instruction::DUP2 << eth::Instruction::SSTORE
                << u256(1) << eth::Instruction::ADD;
        m_context << u256(0) << eth::Instruction::SWAP1 << eth::Instruction::SSTORE;
    }
    else if (!_type.baseType()->isValueType() && _type.length() <= 4)
    {
        // unroll loop for small arrays @todo choose a good value
        solAssert(_type.baseType()->storageBytes() >= 32, "Invalid storage size.");
        for (unsigned i = 1; i < _type.length(); ++i)
        {
            m_context << u256(0);
            StorageItem(m_context, *_type.baseType()).setToZero(SourceLocation(), false);
            m_context
                << eth::Instruction::POP
                << u256(_type.baseType()->storageSize()) << eth::Instruction::ADD;
        }
        m_context << u256(0);
        StorageItem(m_context, *_type.baseType()).setToZero(SourceLocation(), true);
    }
    else
    {
        m_context << eth::Instruction::DUP1 << _type.length();
        convertLengthToSize(_type);
        m_context << eth::Instruction::ADD << eth::Instruction::SWAP1;
        if (_type.baseType()->storageBytes() < 32)
            clearStorageLoop(IntegerType(256));
        else
            clearStorageLoop(*_type.baseType());
        m_context << eth::Instruction::POP;
    }
    solAssert(m_context.stackHeight() == stackHeightStart - 2, "");
}

void ArrayUtils::clearDynamicArray(ArrayType const& _type) const
{
    solAssert(_type.location() == DataLocation::Storage, "");
    solAssert(_type.isDynamicallySized(), "");

    // fetch length
    retrieveLength(_type);
    // set length to zero
    m_context << u256(0) << eth::Instruction::DUP3 << eth::Instruction::SSTORE;
    // Special case: short byte arrays are stored togeher with their length
    eth::AssemblyItem endTag = m_context.newTag();
    if (_type.isByteArray())
    {
        // stack: ref old_length
        m_context << eth::Instruction::DUP1 << u256(31) << eth::Instruction::LT;
        eth::AssemblyItem longByteArray = m_context.appendConditionalJump();
        m_context << eth::Instruction::POP;
        m_context.appendJumpTo(endTag);
        m_context.adjustStackOffset(1); // needed because of jump
        m_context << longByteArray;
    }
    // stack: ref old_length
    convertLengthToSize(_type);
    // compute data positions
    m_context << eth::Instruction::SWAP1;
    CompilerUtils(m_context).computeHashStatic();
    // stack: len data_pos
    m_context << eth::Instruction::SWAP1 << eth::Instruction::DUP2 << eth::Instruction::ADD
        << eth::Instruction::SWAP1;
    // stack: data_pos_end data_pos
    if (_type.isByteArray() || _type.baseType()->storageBytes() < 32)
        clearStorageLoop(IntegerType(256));
    else
        clearStorageLoop(*_type.baseType());
    // cleanup
    m_context << endTag;
    m_context << eth::Instruction::POP;
}

void ArrayUtils::resizeDynamicArray(ArrayType const& _type) const
{
    solAssert(_type.location() == DataLocation::Storage, "");
    solAssert(_type.isDynamicallySized(), "");
    if (!_type.isByteArray() && _type.baseType()->storageBytes() < 32)
        solAssert(_type.baseType()->isValueType(), "Invalid storage size for non-value type.");

    unsigned stackHeightStart = m_context.stackHeight();
    eth::AssemblyItem resizeEnd = m_context.newTag();

    // stack: ref new_length
    // fetch old length
    retrieveLength(_type, 1);
    // stack: ref new_length old_length
    solAssert(m_context.stackHeight() - stackHeightStart == 3 - 2, "2");

    // Special case for short byte arrays, they are stored together with their length
    if (_type.isByteArray())
    {
        eth::AssemblyItem regularPath = m_context.newTag();
        // We start by a large case-distinction about the old and new length of the byte array.

        m_context << eth::Instruction::DUP3 << eth::Instruction::SLOAD;
        // stack: ref new_length current_length ref_value

        solAssert(m_context.stackHeight() - stackHeightStart == 4 - 2, "3");
        m_context << eth::Instruction::DUP2 << u256(31) << eth::Instruction::LT;
        eth::AssemblyItem currentIsLong = m_context.appendConditionalJump();
        m_context << eth::Instruction::DUP3 << u256(31) << eth::Instruction::LT;
        eth::AssemblyItem newIsLong = m_context.appendConditionalJump();

        // Here: short -> short

        // Compute 1 << (256 - 8 * new_size)
        eth::AssemblyItem shortToShort = m_context.newTag();
        m_context << shortToShort;
        m_context << eth::Instruction::DUP3 << u256(8) << eth::Instruction::MUL;
        m_context << u256(0x100) << eth::Instruction::SUB;
        m_context << u256(2) << eth::Instruction::EXP;
        // Divide and multiply by that value, clearing bits.
        m_context << eth::Instruction::DUP1 << eth::Instruction::SWAP2;
        m_context << eth::Instruction::DIV << eth::Instruction::MUL;
        // Insert 2*length.
        m_context << eth::Instruction::DUP3 << eth::Instruction::DUP1 << eth::Instruction::ADD;
        m_context << eth::Instruction::OR;
        // Store.
        m_context << eth::Instruction::DUP4 << eth::Instruction::SSTORE;
        solAssert(m_context.stackHeight() - stackHeightStart == 3 - 2, "3");
        m_context.appendJumpTo(resizeEnd);

        m_context.adjustStackOffset(1); // we have to do that because of the jumps
        // Here: short -> long

        m_context << newIsLong;
        // stack: ref new_length current_length ref_value
        solAssert(m_context.stackHeight() - stackHeightStart == 4 - 2, "3");
        // Zero out lower-order byte.
        m_context << u256(0xff) << eth::Instruction::NOT << eth::Instruction::AND;
        // Store at data location.
        m_context << eth::Instruction::DUP4;
        CompilerUtils(m_context).computeHashStatic();
        m_context << eth::Instruction::SSTORE;
        // stack: ref new_length current_length
        // Store new length: Compule 2*length + 1 and store it.
        m_context << eth::Instruction::DUP2 << eth::Instruction::DUP1 << eth::Instruction::ADD;
        m_context << u256(1) << eth::Instruction::ADD;
        // stack: ref new_length current_length 2*new_length+1
        m_context << eth::Instruction::DUP4 << eth::Instruction::SSTORE;
        solAssert(m_context.stackHeight() - stackHeightStart == 3 - 2, "3");
        m_context.appendJumpTo(resizeEnd);

        m_context.adjustStackOffset(1); // we have to do that because of the jumps

        m_context << currentIsLong;
        m_context << eth::Instruction::DUP3 << u256(31) << eth::Instruction::LT;
        m_context.appendConditionalJumpTo(regularPath);

        // Here: long -> short
        // Read the first word of the data and store it on the stack. Clear the data location and
        // then jump to the short -> short case.

        // stack: ref new_length current_length ref_value
        solAssert(m_context.stackHeight() - stackHeightStart == 4 - 2, "3");
        m_context << eth::Instruction::POP << eth::Instruction::DUP3;
        CompilerUtils(m_context).computeHashStatic();
        m_context << eth::Instruction::DUP1 << eth::Instruction::SLOAD << eth::Instruction::SWAP1;
        // stack: ref new_length current_length first_word data_location
        m_context << eth::Instruction::DUP3;
        convertLengthToSize(_type);
        m_context << eth::Instruction::DUP2 << eth::Instruction::ADD << eth::Instruction::SWAP1;
        // stack: ref new_length current_length first_word data_location_end data_location
        clearStorageLoop(IntegerType(256));
        m_context << eth::Instruction::POP;
        // stack: ref new_length current_length first_word
        solAssert(m_context.stackHeight() - stackHeightStart == 4 - 2, "3");
        m_context.appendJumpTo(shortToShort);

        m_context << regularPath;
        // stack: ref new_length current_length ref_value
        m_context << eth::Instruction::POP;
    }

    // Change of length for a regular array (i.e. length at location, data at sha3(location)).
    // stack: ref new_length old_length
    // store new length
    m_context << eth::Instruction::DUP2;
    if (_type.isByteArray())
        // For a "long" byte array, store length as 2*length+1
        m_context << eth::Instruction::DUP1 << eth::Instruction::ADD << u256(1) << eth::Instruction::ADD;
    m_context<< eth::Instruction::DUP4 << eth::Instruction::SSTORE;
    // skip if size is not reduced
    m_context << eth::Instruction::DUP2 << eth::Instruction::DUP2
        << eth::Instruction::ISZERO << eth::Instruction::GT;
    m_context.appendConditionalJumpTo(resizeEnd);

    // size reduced, clear the end of the array
    // stack: ref new_length old_length
    convertLengthToSize(_type);
    m_context << eth::Instruction::DUP2;
    convertLengthToSize(_type);
    // stack: ref new_length old_size new_size
    // compute data positions
    m_context << eth::Instruction::DUP4;
    CompilerUtils(m_context).computeHashStatic();
    // stack: ref new_length old_size new_size data_pos
    m_context << eth::Instruction::SWAP2 << eth::Instruction::DUP3 << eth::Instruction::ADD;
    // stack: ref new_length data_pos new_size delete_end
    m_context << eth::Instruction::SWAP2 << eth::Instruction::ADD;
    // stack: ref new_length delete_end delete_start
    if (_type.isByteArray() || _type.baseType()->storageBytes() < 32)
        clearStorageLoop(IntegerType(256));
    else
        clearStorageLoop(*_type.baseType());

    m_context << resizeEnd;
    // cleanup
    m_context << eth::Instruction::POP << eth::Instruction::POP << eth::Instruction::POP;
    solAssert(m_context.stackHeight() == stackHeightStart - 2, "");
}

void ArrayUtils::clearStorageLoop(Type const& _type) const
{
    unsigned stackHeightStart = m_context.stackHeight();
    if (_type.category() == Type::Category::Mapping)
    {
        m_context << eth::Instruction::POP;
        return;
    }
    // stack: end_pos pos

    // jump to and return from the loop to allow for duplicate code removal
    eth::AssemblyItem returnTag = m_context.pushNewTag();
    m_context << eth::Instruction::SWAP2 << eth::Instruction::SWAP1;

    // stack: <return tag> end_pos pos
    eth::AssemblyItem loopStart = m_context.appendJumpToNew();
    m_context << loopStart;
    // check for loop condition
    m_context << eth::Instruction::DUP1 << eth::Instruction::DUP3
               << eth::Instruction::GT << eth::Instruction::ISZERO;
    eth::AssemblyItem zeroLoopEnd = m_context.newTag();
    m_context.appendConditionalJumpTo(zeroLoopEnd);
    // delete
    m_context << u256(0);
    StorageItem(m_context, _type).setToZero(SourceLocation(), false);
    m_context << eth::Instruction::POP;
    // increment
    m_context << u256(1) << eth::Instruction::ADD;
    m_context.appendJumpTo(loopStart);
    // cleanup
    m_context << zeroLoopEnd;
    m_context << eth::Instruction::POP << eth::Instruction::SWAP1;
    // "return"
    m_context << eth::Instruction::JUMP;

    m_context << returnTag;
    solAssert(m_context.stackHeight() == stackHeightStart - 1, "");
}

void ArrayUtils::convertLengthToSize(ArrayType const& _arrayType, bool _pad) const
{
    if (_arrayType.location() == DataLocation::Storage)
    {
        if (_arrayType.baseType()->storageSize() <= 1)
        {
            unsigned baseBytes = _arrayType.baseType()->storageBytes();
            if (baseBytes == 0)
                m_context << eth::Instruction::POP << u256(1);
            else if (baseBytes <= 16)
            {
                unsigned itemsPerSlot = 32 / baseBytes;
                m_context
                    << u256(itemsPerSlot - 1) << eth::Instruction::ADD
                    << u256(itemsPerSlot) << eth::Instruction::SWAP1 << eth::Instruction::DIV;
            }
        }
        else
            m_context << _arrayType.baseType()->storageSize() << eth::Instruction::MUL;
    }
    else
    {
        if (!_arrayType.isByteArray())
        {
            if (_arrayType.location() == DataLocation::Memory)
                m_context << _arrayType.baseType()->memoryHeadSize();
            else
                m_context << _arrayType.baseType()->calldataEncodedSize();
            m_context << eth::Instruction::MUL;
        }
        else if (_pad)
            m_context << u256(31) << eth::Instruction::ADD
                << u256(32) << eth::Instruction::DUP1
                << eth::Instruction::SWAP2 << eth::Instruction::DIV << eth::Instruction::MUL;
    }
}

void ArrayUtils::retrieveLength(ArrayType const& _arrayType, unsigned _stackDepth) const
{
    if (!_arrayType.isDynamicallySized())
        m_context << _arrayType.length();
    else
    {
        m_context << eth::dupInstruction(1 + _stackDepth);
        switch (_arrayType.location())
        {
        case DataLocation::CallData:
            // length is stored on the stack
            break;
        case DataLocation::Memory:
            m_context << eth::Instruction::MLOAD;
            break;
        case DataLocation::Storage:
            m_context << eth::Instruction::SLOAD;
            if (_arrayType.isByteArray())
            {
                // Retrieve length both for in-place strings and off-place strings:
                // Computes (x & (0x100 * (ISZERO (x & 1)) - 1)) / 2
                // i.e. for short strings (x & 1 == 0) it does (x & 0xff) / 2 and for long strings it
                // computes (x & (-1)) / 2, which is equivalent to just x / 2.
                m_context << u256(1) << eth::Instruction::DUP2 << u256(1) << eth::Instruction::AND;
                m_context << eth::Instruction::ISZERO << u256(0x100) << eth::Instruction::MUL;
                m_context << eth::Instruction::SUB << eth::Instruction::AND;
                m_context << u256(2) << eth::Instruction::SWAP1 << eth::Instruction::DIV;
            }
            break;
        }
    }
}

void ArrayUtils::accessIndex(ArrayType const& _arrayType, bool _doBoundsCheck) const
{
    /// Stack: reference [length] index
    DataLocation location = _arrayType.location();

    if (_doBoundsCheck)
    {
        // retrieve length
        ArrayUtils::retrieveLength(_arrayType, 1);
        // Stack: ref [length] index length
        // check out-of-bounds access
        m_context << eth::Instruction::DUP2 << eth::Instruction::LT << eth::Instruction::ISZERO;
        // out-of-bounds access throws exception
        m_context.appendConditionalJumpTo(m_context.errorTag());
    }
    if (location == DataLocation::CallData && _arrayType.isDynamicallySized())
        // remove length if present
        m_context << eth::Instruction::SWAP1 << eth::Instruction::POP;

    // stack: <base_ref> <index>
    m_context << eth::Instruction::SWAP1;
    // stack: <index> <base_ref>
    switch (location)
    {
    case DataLocation::Memory:
        if (_arrayType.isDynamicallySized())
            m_context << u256(32) << eth::Instruction::ADD;
        // fall-through
    case DataLocation::CallData:
        if (!_arrayType.isByteArray())
        {
            m_context << eth::Instruction::SWAP1;
            if (location == DataLocation::CallData)
                m_context << _arrayType.baseType()->calldataEncodedSize();
            else
                m_context << u256(_arrayType.memoryHeadSize());
            m_context << eth::Instruction::MUL;
        }
        m_context << eth::Instruction::ADD;
        break;
    case DataLocation::Storage:
    {
        eth::AssemblyItem endTag = m_context.newTag();
        if (_arrayType.isByteArray())
        {
            // Special case of short byte arrays.
            m_context << eth::Instruction::SWAP1;
            m_context << eth::Instruction::DUP2 << eth::Instruction::SLOAD;
            m_context << u256(1) << eth::Instruction::AND << eth::Instruction::ISZERO;
            // No action needed for short byte arrays.
            m_context.appendConditionalJumpTo(endTag);
            m_context << eth::Instruction::SWAP1;
        }
        if (_arrayType.isDynamicallySized())
            CompilerUtils(m_context).computeHashStatic();
        m_context << eth::Instruction::SWAP1;
        if (_arrayType.baseType()->storageBytes() <= 16)
        {
            // stack: <data_ref> <index>
            // goal:
            // <ref> <byte_number> = <base_ref + index / itemsPerSlot> <(index % itemsPerSlot) * byteSize>
            unsigned byteSize = _arrayType.baseType()->storageBytes();
            solAssert(byteSize != 0, "");
            unsigned itemsPerSlot = 32 / byteSize;
            m_context << u256(itemsPerSlot) << eth::Instruction::SWAP2;
            // stack: itemsPerSlot index data_ref
            m_context
                << eth::Instruction::DUP3 << eth::Instruction::DUP3
                << eth::Instruction::DIV << eth::Instruction::ADD
            // stack: itemsPerSlot index (data_ref + index / itemsPerSlot)
                << eth::Instruction::SWAP2 << eth::Instruction::SWAP1
                << eth::Instruction::MOD;
            if (byteSize != 1)
                m_context << u256(byteSize) << eth::Instruction::MUL;
        }
        else
        {
            if (_arrayType.baseType()->storageSize() != 1)
                m_context << _arrayType.baseType()->storageSize() << eth::Instruction::MUL;
            m_context << eth::Instruction::ADD << u256(0);
        }
        m_context << endTag;
        break;
    }
    default:
        solAssert(false, "");
    }
}

void ArrayUtils::incrementByteOffset(unsigned _byteSize, unsigned _byteOffsetPosition, unsigned _storageOffsetPosition) const
{
    solAssert(_byteSize < 32, "");
    solAssert(_byteSize != 0, "");
    // We do the following, but avoiding jumps:
    // byteOffset += byteSize
    // if (byteOffset + byteSize > 32)
    // {
    //     storageOffset++;
    //     byteOffset = 0;
    // }
    if (_byteOffsetPosition > 1)
        m_context << eth::swapInstruction(_byteOffsetPosition - 1);
    m_context << u256(_byteSize) << eth::Instruction::ADD;
    if (_byteOffsetPosition > 1)
        m_context << eth::swapInstruction(_byteOffsetPosition - 1);
    // compute, X := (byteOffset + byteSize - 1) / 32, should be 1 iff byteOffset + bytesize > 32
    m_context
        << u256(32) << eth::dupInstruction(1 + _byteOffsetPosition) << u256(_byteSize - 1)
        << eth::Instruction::ADD << eth::Instruction::DIV;
    // increment storage offset if X == 1 (just add X to it)
    // stack: X
    m_context
        << eth::swapInstruction(_storageOffsetPosition) << eth::dupInstruction(_storageOffsetPosition + 1)
        << eth::Instruction::ADD << eth::swapInstruction(_storageOffsetPosition);
    // stack: X
    // set source_byte_offset to zero if X == 1 (using source_byte_offset *= 1 - X)
    m_context << u256(1) << eth::Instruction::SUB;
    // stack: 1 - X
    if (_byteOffsetPosition == 1)
        m_context << eth::Instruction::MUL;
    else
        m_context
            << eth::dupInstruction(_byteOffsetPosition + 1) << eth::Instruction::MUL
            << eth::swapInstruction(_byteOffsetPosition) << eth::Instruction::POP;
}