Source/JavaScriptCore/bytecode/UnlinkedInstructionStream.h

/*
 * Copyright (C) 2014 Apple Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */


#pragma once

#include "Opcode.h"
#include "UnlinkedCodeBlock.h"
#include <wtf/RefCountedArray.h>

namespace JSC {

class UnlinkedInstructionStream {
    WTF_MAKE_FAST_ALLOCATED;
public:
    explicit UnlinkedInstructionStream(const Vector<UnlinkedInstruction, 0, UnsafeVectorOverflow>&);

    unsigned count() const { return m_instructionCount; }
    size_t sizeInBytes() const;

    class Reader {
    public:
        explicit Reader(const UnlinkedInstructionStream&);

        const UnlinkedInstruction* next();
        bool atEnd() const { return m_index == m_stream.m_data.size(); }

    private:
        unsigned char read8();
        unsigned read32();

        const UnlinkedInstructionStream& m_stream;
        UnlinkedInstruction m_unpackedBuffer[16];
        unsigned m_index;
    };

#ifndef NDEBUG
    const RefCountedArray<UnlinkedInstruction>& unpackForDebugging() const;
#endif

private:
    friend class Reader;

#ifndef NDEBUG
    mutable RefCountedArray<UnlinkedInstruction> m_unpackedInstructionsForDebugging;
#endif

    RefCountedArray<unsigned char> m_data;
    unsigned m_instructionCount;
};

// Unlinked instructions are packed in a simple stream format.
//
// The first byte is always the opcode.
// It's followed by an opcode-dependent number of argument values.
// The first 3 bits of each value determines the format:
//
//     5-bit positive integer (1 byte total)
//     5-bit negative integer (1 byte total)
//     13-bit positive integer (2 bytes total)
//     13-bit negative integer (2 bytes total)
//     5-bit constant register index, based at 0x40000000 (1 byte total)
//     13-bit constant register index, based at 0x40000000 (2 bytes total)
//     32-bit raw value (5 bytes total)

enum PackedValueType {
    Positive5Bit = 0,
    Negative5Bit,
    Positive13Bit,
    Negative13Bit,
    ConstantRegister5Bit,
    ConstantRegister13Bit,
    Full32Bit
};

ALWAYS_INLINE UnlinkedInstructionStream::Reader::Reader(const UnlinkedInstructionStream& stream)
    : m_stream(stream)
    , m_index(0)
{
}

ALWAYS_INLINE unsigned char UnlinkedInstructionStream::Reader::read8()
{
    return m_stream.m_data.data()[m_index++];
}

ALWAYS_INLINE unsigned UnlinkedInstructionStream::Reader::read32()
{
    const unsigned char* data = &m_stream.m_data.data()[m_index];
    unsigned char type = data[0] >> 5;

    switch (type) {
    case Positive5Bit:
        m_index++;
        return data[0];
    case Negative5Bit:
        m_index++;
        return 0xffffffe0 | data[0];
    case Positive13Bit:
        m_index += 2;
        return ((data[0] & 0x1F) << 8) | data[1];
    case Negative13Bit:
        m_index += 2;
        return 0xffffe000 | ((data[0] & 0x1F) << 8) | data[1];
    case ConstantRegister5Bit:
        m_index++;
        return 0x40000000 | (data[0] & 0x1F);
    case ConstantRegister13Bit:
        m_index += 2;
        return 0x40000000 | ((data[0] & 0x1F) << 8) | data[1];
    default:
        ASSERT(type == Full32Bit);
        m_index += 5;
        return data[1] | data[2] << 8 | data[3] << 16 | data[4] << 24;
    }
}

ALWAYS_INLINE const UnlinkedInstruction* UnlinkedInstructionStream::Reader::next()
{
    m_unpackedBuffer[0].u.opcode = static_cast<OpcodeID>(read8());
    unsigned opLength = opcodeLength(m_unpackedBuffer[0].u.opcode);
    for (unsigned i = 1; i < opLength; ++i)
        m_unpackedBuffer[i].u.unsignedValue = read32();
    return m_unpackedBuffer;
}

} // namespace JSC