/*

 * Copyright (c) 2015, 2015, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code 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

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package org.graalvm.compiler.core.common.util;

import static org.graalvm.compiler.core.common.util.UnsafeAccess.UNSAFE;

import sun.misc.Unsafe;

/**

 * Provides low-level read access from a byte[] array for signed and unsigned values of size 1, 2,

 * 4, and 8 bytes.

 *

 * The class can either be instantiated for sequential access to the byte[] array; or static methods

 * can be used to read values without the overhead of creating an instance.

 *

 * The flag {@code supportsUnalignedMemoryAccess} must be set according to the capabilities of the

 * hardware architecture: the value {@code true} allows more efficient memory access on

 * architectures that support unaligned memory accesses; the value {@code false} is the safe

 * fallback that works on every hardware.

 */

public abstract class UnsafeArrayTypeReader implements TypeReader {

    public static int getS1(byte[] data, long byteIndex) {

        return UNSAFE.getByte(data, readOffset(data, byteIndex, Byte.BYTES));

    }

    public static int getU1(byte[] data, long byteIndex) {

        return UNSAFE.getByte(data, readOffset(data, byteIndex, Byte.BYTES)) & 0xFF;

    }

    public static int getS2(byte[] data, long byteIndex, boolean supportsUnalignedMemoryAccess) {

        if (supportsUnalignedMemoryAccess) {

            return UnalignedUnsafeArrayTypeReader.getS2(data, byteIndex);

        } else {

            return AlignedUnsafeArrayTypeReader.getS2(data, byteIndex);

        }

    }

    public static int getU2(byte[] data, long byteIndex, boolean supportsUnalignedMemoryAccess) {

        return getS2(data, byteIndex, supportsUnalignedMemoryAccess) & 0xFFFF;

    }

    public static int getS4(byte[] data, long byteIndex, boolean supportsUnalignedMemoryAccess) {

        if (supportsUnalignedMemoryAccess) {

            return UnalignedUnsafeArrayTypeReader.getS4(data, byteIndex);

        } else {

            return AlignedUnsafeArrayTypeReader.getS4(data, byteIndex);

        }

    }

    public static long getU4(byte[] data, long byteIndex, boolean supportsUnalignedMemoryAccess) {

        return getS4(data, byteIndex, supportsUnalignedMemoryAccess) & 0xFFFFFFFFL;

    }

    public static long getS8(byte[] data, long byteIndex, boolean supportsUnalignedMemoryAccess) {

        if (supportsUnalignedMemoryAccess) {

            return UnalignedUnsafeArrayTypeReader.getS8(data, byteIndex);

        } else {

            return AlignedUnsafeArrayTypeReader.getS8(data, byteIndex);

        }

    }

    protected static long readOffset(byte[] data, long byteIndex, int numBytes) {

        assert byteIndex >= 0;

        assert numBytes > 0;

        assert byteIndex + numBytes <= data.length;

        assert Unsafe.ARRAY_BYTE_INDEX_SCALE == 1;

        return byteIndex + Unsafe.ARRAY_BYTE_BASE_OFFSET;

    }

    public static UnsafeArrayTypeReader create(byte[] data, long byteIndex, boolean supportsUnalignedMemoryAccess) {

        if (supportsUnalignedMemoryAccess) {

            return new UnalignedUnsafeArrayTypeReader(data, byteIndex);

        } else {

            return new AlignedUnsafeArrayTypeReader(data, byteIndex);

        }

    }

    protected final byte[] data;

    protected long byteIndex;

    protected UnsafeArrayTypeReader(byte[] data, long byteIndex) {

        this.data = data;

        this.byteIndex = byteIndex;

    }

    @Override

    public long getByteIndex() {

        return byteIndex;

    }

    @Override

    public void setByteIndex(long byteIndex) {

        this.byteIndex = byteIndex;

    }

    @Override

    public final int getS1() {

        int result = getS1(data, byteIndex);

        byteIndex += Byte.BYTES;

        return result;

    }

    @Override

    public final int getU1() {

        int result = getU1(data, byteIndex);

        byteIndex += Byte.BYTES;

        return result;

    }

    @Override

    public final int getU2() {

        return getS2() & 0xFFFF;

    }

    @Override

    public final long getU4() {

        return getS4() & 0xFFFFFFFFL;

    }

}

final class UnalignedUnsafeArrayTypeReader extends UnsafeArrayTypeReader {

    protected static int getS2(byte[] data, long byteIndex) {

        return UNSAFE.getShort(data, readOffset(data, byteIndex, Short.BYTES));

    }

    protected static int getS4(byte[] data, long byteIndex) {

        return UNSAFE.getInt(data, readOffset(data, byteIndex, Integer.BYTES));

    }

    protected static long getS8(byte[] data, long byteIndex) {

        return UNSAFE.getLong(data, readOffset(data, byteIndex, Long.BYTES));

    }

    protected UnalignedUnsafeArrayTypeReader(byte[] data, long byteIndex) {

        super(data, byteIndex);

    }

    @Override

    public int getS2() {

        int result = getS2(data, byteIndex);

        byteIndex += Short.BYTES;

        return result;

    }

    @Override

    public int getS4() {

        int result = getS4(data, byteIndex);

        byteIndex += Integer.BYTES;

        return result;

    }

    @Override

    public long getS8() {

        long result = getS8(data, byteIndex);

        byteIndex += Long.BYTES;

        return result;

    }

}

class AlignedUnsafeArrayTypeReader extends UnsafeArrayTypeReader {

    protected static int getS2(byte[] data, long byteIndex) {

        long offset = readOffset(data, byteIndex, Short.BYTES);

        return ((UNSAFE.getByte(data, offset + 0) & 0xFF) << 0) | //

                        (UNSAFE.getByte(data, offset + 1) << 8);

    }

    protected static int getS4(byte[] data, long byteIndex) {

        long offset = readOffset(data, byteIndex, Integer.BYTES);

        return ((UNSAFE.getByte(data, offset + 0) & 0xFF) << 0) | //

                        ((UNSAFE.getByte(data, offset + 1) & 0xFF) << 8) | //

                        ((UNSAFE.getByte(data, offset + 2) & 0xFF) << 16) | //

                        (UNSAFE.getByte(data, offset + 3) << 24);

    }

    protected static long getS8(byte[] data, long byteIndex) {

        long offset = readOffset(data, byteIndex, Long.BYTES);

        return ((long) ((UNSAFE.getByte(data, offset + 0) & 0xFF)) << 0) | //

                        ((long) ((UNSAFE.getByte(data, offset + 1) & 0xFF)) << 8) | //

                        ((long) ((UNSAFE.getByte(data, offset + 2) & 0xFF)) << 16) | //

                        ((long) ((UNSAFE.getByte(data, offset + 3) & 0xFF)) << 24) | //

                        ((long) ((UNSAFE.getByte(data, offset + 4) & 0xFF)) << 32) | //

                        ((long) ((UNSAFE.getByte(data, offset + 5) & 0xFF)) << 40) | //

                        ((long) ((UNSAFE.getByte(data, offset + 6) & 0xFF)) << 48) | //

                        ((long) (UNSAFE.getByte(data, offset + 7)) << 56);

    }

    protected AlignedUnsafeArrayTypeReader(byte[] data, long byteIndex) {

        super(data, byteIndex);

    }

    @Override

    public int getS2() {

        int result = getS2(data, byteIndex);

        byteIndex += Short.BYTES;

        return result;

    }

    @Override

    public int getS4() {

        int result = getS4(data, byteIndex);

        byteIndex += Integer.BYTES;

        return result;

    }

    @Override

    public long getS8() {

        long result = getS8(data, byteIndex);

        byteIndex += Long.BYTES;

        return result;

    }

}