/*
 * 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;
    }
}