Value.hpp

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/* src/vm/jit/loop/Value.hpp

   Copyright (C) 1996-2012
   CACAOVM - Verein zur Foerderung der freien virtuellen Maschine CACAO

   This file is part of CACAO.

   This program 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 2, or (at
   your option) any later version.

   This program 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 this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
   02110-1301, USA.

*/

#ifndef _VALUE_HPP
#define _VALUE_HPP

#include <limits>

#include "vm/types.hpp"

/**
 * Represents the result of the addition of a certain IR-variable with a certain constant.
 * The addition may overflow.
 */
class Value
{
    s4 _variable;   // If _variable == -1, this value is considered as "unknown".
    s4 _constant;

    /**
     * Initializes this value with (variable + constant).
     */
    Value(s4 variable, s4 constant)
        : _variable(variable)
        , _constant(constant)
    {}

public:

    static Value newAddition(s4 variable, s4 constant);
    static Value newUnknown();

    s4 variable() const;
    s4 constant() const;

    bool isUnknown() const;

    /**
     * Adds a constant to this value.
     * If this value is "unknown", it stays unknown.
     */
    void addConstant(s4 constant);

    /**
     * Subtracts a constant from this value.
     * If this value is "unknown", it stays unknown.
     */
    void subtractConstant(s4 constant);
};

inline Value Value::newAddition(s4 variable, s4 constant)
{
    assert(variable != -1);
    return Value(variable, constant);
}

inline Value Value::newUnknown()
{
    return Value(-1, 0);
}

inline s4 Value::variable() const
{
    assert(_variable != -1);
    return _variable;
}

inline s4 Value::constant() const
{
    return _constant;
}

inline bool Value::isUnknown() const
{
    return _variable == -1;
}

inline void Value::addConstant(s4 constant)
{
    s8 sum = static_cast<s8>(_constant) + constant;
    if (std::numeric_limits<s4>::min() <= sum && sum <= std::numeric_limits<s4>::max())
        _constant = static_cast<s4>(sum);
    else
        _variable = -1;   // In case of an overflow, we get an "unknown" value.
}

inline void Value::subtractConstant(s4 constant)
{
    s8 sum = static_cast<s8>(_constant) - constant;
    if (std::numeric_limits<s4>::min() <= sum && sum <= std::numeric_limits<s4>::max())
        _constant = static_cast<s4>(sum);
    else
        _variable = -1;   // In case of an overflow, we get an "unknown" value.
}

#endif

/*
 * These are local overrides for various environment variables in Emacs.
 * Please do not remove this and leave it at the end of the file, where
 * Emacs will automagically detect them.
 * ---------------------------------------------------------------------
 * Local variables:
 * mode: c++
 * indent-tabs-mode: t
 * c-basic-offset: 4
 * tab-width: 4
 * End:
 * vim:noexpandtab:sw=4:ts=4:
 */