path: root/libsolidity/LValue.h

/*
    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
 * LValues for use in the expresison compiler.
 */

#pragma once

#include <memory>
#include <libevmasm/SourceLocation.h>
#include <libsolidity/ArrayUtils.h>

namespace dev
{
namespace solidity
{

class Declaration;
class Type;
class ArrayType;
class CompilerContext;

/**
 * Abstract class used to retrieve, delete and store data in lvalues/variables.
 */
class LValue
{
protected:
    LValue(CompilerContext& _compilerContext, Type const& _dataType):
        m_context(_compilerContext), m_dataType(_dataType) {}

public:
    /// @returns the number of stack slots occupied by the lvalue reference
    virtual unsigned sizeOnStack() const { return 1; }
    /// Copies the value of the current lvalue to the top of the stack and, if @a _remove is true,
    /// also removes the reference from the stack.
    /// @a _location source location of the current expression, used for error reporting.
    virtual void retrieveValue(SourceLocation const& _location, bool _remove = false) const = 0;
    /// Moves a value from the stack to the lvalue. Removes the value if @a _move is true.
    /// @a _location is the source location of the expression that caused this operation.
    /// Stack pre: value [lvalue_ref]
    /// Stack post: if !_move: value_of(lvalue_ref)
    virtual void storeValue(Type const& _sourceType,
        SourceLocation const& _location = SourceLocation(), bool _move = false) const = 0;
    /// Stores zero in the lvalue. Removes the reference from the stack if @a _removeReference is true.
    /// @a _location is the source location of the requested operation
    virtual void setToZero(
        SourceLocation const& _location = SourceLocation(),
        bool _removeReference = true
    ) const = 0;

protected:
    CompilerContext& m_context;
    Type const& m_dataType;
};

/**
 * Local variable that is completely stored on the stack.
 */
class StackVariable: public LValue
{
public:
    StackVariable(CompilerContext& _compilerContext, Declaration const& _declaration);

    virtual unsigned sizeOnStack() const override { return 0; }
    virtual void retrieveValue(SourceLocation const& _location, bool _remove = false) const override;
    virtual void storeValue(
        Type const& _sourceType,
        SourceLocation const& _location = SourceLocation(),
        bool _move = false
    ) const override;
    virtual void setToZero(
        SourceLocation const& _location = SourceLocation(),
        bool _removeReference = true
    ) const override;

private:
    /// Base stack offset (@see CompilerContext::getBaseStackOffsetOfVariable) of the local variable.
    unsigned m_baseStackOffset;
    /// Number of stack elements occupied by the value (not the reference).
    unsigned m_size;
};

/**
 * Reference to some item in memory.
 */
class MemoryItem: public LValue
{
public:
    MemoryItem(CompilerContext& _compilerContext, Type const& _type, bool _padded = true);
    virtual unsigned sizeOnStack() const override { return 1; }
    virtual void retrieveValue(SourceLocation const& _location, bool _remove = false) const override;
    virtual void storeValue(
        Type const& _sourceType,
        SourceLocation const& _location = SourceLocation(),
        bool _move = false
    ) const override;
    virtual void setToZero(
        SourceLocation const& _location = SourceLocation(),
        bool _removeReference = true
    ) const override;
private:
    /// Special flag to deal with byte array elements.
    bool m_padded = false;
};

/**
 * Reference to some item in storage. On the stack this is <storage key> <offset_inside_value>,
 * where 0 <= offset_inside_value < 32 and an offset of i means that the value is multiplied
 * by 2**i before storing it.
 */
class StorageItem: public LValue
{
public:
    /// Constructs the LValue and pushes the location of @a _declaration onto the stack.
    StorageItem(CompilerContext& _compilerContext, Declaration const& _declaration);
    /// Constructs the LValue and assumes that the storage reference is already on the stack.
    StorageItem(CompilerContext& _compilerContext, Type const& _type);
    virtual unsigned sizeOnStack() const override { return 2; }
    virtual void retrieveValue(SourceLocation const& _location, bool _remove = false) const override;
    virtual void storeValue(
        Type const& _sourceType,
        SourceLocation const& _location = SourceLocation(),
        bool _move = false
    ) const override;
    virtual void setToZero(
        SourceLocation const& _location = SourceLocation(),
        bool _removeReference = true
    ) const override;
};

/**
 * Reference to a single byte inside a storage byte array.
 * Stack: <storage_ref> <byte_number>
 */
class StorageByteArrayElement: public LValue
{
public:
    /// Constructs the LValue and assumes that the storage reference is already on the stack.
    StorageByteArrayElement(CompilerContext& _compilerContext);
    virtual unsigned sizeOnStack() const override { return 2; }
    virtual void retrieveValue(SourceLocation const& _location, bool _remove = false) const override;
    virtual void storeValue(
        Type const& _sourceType,
        SourceLocation const& _location = SourceLocation(),
        bool _move = false
    ) const override;
    virtual void setToZero(
        SourceLocation const& _location = SourceLocation(),
        bool _removeReference = true
    ) const override;
};

/**
 * Reference to the "length" member of a dynamically-sized array. This is an LValue with special
 * semantics since assignments to it might reduce its length and thus arrays members have to be
 * deleted.
 */
class StorageArrayLength: public LValue
{
public:
    /// Constructs the LValue, assumes that the reference to the array head is already on the stack.
    StorageArrayLength(CompilerContext& _compilerContext, ArrayType const& _arrayType);
    virtual void retrieveValue(SourceLocation const& _location, bool _remove = false) const override;
    virtual void storeValue(
        Type const& _sourceType,
        SourceLocation const& _location = SourceLocation(),
        bool _move = false
    ) const override;
    virtual void setToZero(
        SourceLocation const& _location = SourceLocation(),
        bool _removeReference = true
    ) const override;

private:
    ArrayType const& m_arrayType;
};

}
}