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 * The Universal Permissive License (UPL), Version 1.0
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 * (a) the Software, and
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 * (b) any piece of software and/or hardware listed in the lrgrwrks.txt file if
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 * The above copyright notice and either this complete permission notice or at a
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package com.oracle.truffle.js.runtime.array;

import java.lang.invoke.VarHandle;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;

public abstract class ByteBufferAccess {

    @SuppressWarnings("static-method")
    public final int getInt8(ByteBuffer buffer, int index) {
        return buffer.get(index);
    }

    public final int getUint8(ByteBuffer buffer, int index) {
        return getInt8(buffer, index) & 0xff;
    }

    public abstract int getInt16(ByteBuffer buffer, int index);

    public final int getUint16(ByteBuffer buffer, int index) {
        return getInt16(buffer, index) & 0xffff;
    }

    public abstract int getInt32(ByteBuffer buffer, int index);

    public final short getFloat16(ByteBuffer buffer, int index) {
        return (short) getInt16(buffer, index);
    }

    public abstract float getFloat(ByteBuffer buffer, int index);

    public abstract double getDouble(ByteBuffer buffer, int index);

    public abstract long getInt64(ByteBuffer buffer, int index);

    @SuppressWarnings("static-method")
    public final void putInt8(ByteBuffer buffer, int index, int value) {
        buffer.put(index, (byte) value);
    }

    public abstract void putInt16(ByteBuffer buffer, int index, int value);

    public abstract void putInt32(ByteBuffer buffer, int index, int value);

    public final void putFloat16(ByteBuffer buffer, int index, short value) {
        putInt16(buffer, index, value);
    }

    public abstract void putFloat(ByteBuffer buffer, int index, float value);

    public abstract void putDouble(ByteBuffer buffer, int index, double value);

    public abstract void putInt64(ByteBuffer buffer, int index, long value);

    public abstract int compareExchangeInt32(ByteBuffer buffer, int index, int expectedValue, int newValue);

    public abstract long compareExchangeInt64(ByteBuffer buffer, int index, long expectedValue, long newValue);

    /**
     * Emulate 8-bit CAS using 32-bit CAS. Cannot be used if the buffer length is not a multiple of
     * 4 and too short for the 32-bit access to be fully in bounds.
     */
    public int compareExchangeInt8(ByteBuffer buffer, int index, int expectedValue, int newValue) {
        int wordOffset = index & ~3;
        assert wordOffset <= buffer.capacity() - Integer.BYTES;
        int shift = (index & 3) << 3;
        if (ByteOrder.nativeOrder() == ByteOrder.BIG_ENDIAN) {
            shift = 24 - shift;
        }
        int mask = 0xFF << shift;
        int maskedExpected = (expectedValue & 0xFF) << shift;
        int maskedReplacement = (newValue & 0xFF) << shift;
        int fullWord;
        int exchanged;
        do {
            fullWord = getInt32(buffer, wordOffset);
            VarHandle.acquireFence();
            if ((fullWord & mask) != maskedExpected) {
                return (byte) ((fullWord & mask) >> shift);
            }
            exchanged = compareExchangeInt32(buffer, wordOffset, fullWord, (fullWord & ~mask) | maskedReplacement);
        } while (exchanged != fullWord);
        return expectedValue;
    }

    /**
     * Emulate 16-bit CAS using 32-bit CAS. Cannot be used if the buffer length is not a multiple of
     * 4 and too short for the 32-bit access to be fully in bounds, or if the index is odd.
     */
    public int compareExchangeInt16(ByteBuffer buffer, int index, int expectedValue, int newValue) {
        assert (index & 1) != 1 : index;
        int wordOffset = index & ~3;
        assert wordOffset <= buffer.capacity() - Integer.BYTES;
        int shift = (index & 2) << 3;
        if (ByteOrder.nativeOrder() == ByteOrder.BIG_ENDIAN) {
            shift = 16 - shift;
        }
        int mask = 0xFFFF << shift;
        int maskedExpected = (expectedValue & 0xFFFF) << shift;
        int maskedReplacement = (newValue & 0xFFFF) << shift;
        int fullWord;
        int exchanged;
        do {
            fullWord = getInt32(buffer, wordOffset);
            VarHandle.acquireFence();
            if ((fullWord & mask) != maskedExpected) {
                return (short) ((fullWord & mask) >> shift);
            }
            exchanged = compareExchangeInt32(buffer, wordOffset, fullWord, (fullWord & ~mask) | maskedReplacement);
        } while (exchanged != fullWord);
        return expectedValue;
    }

    public static final ByteBufferAccess littleEndian() {
        return ByteBufferSupport.littleEndian();
    }

    public static final ByteBufferAccess bigEndian() {
        return ByteBufferSupport.bigEndian();
    }

    public static final ByteBufferAccess nativeOrder() {
        return ByteBufferSupport.nativeOrder();
    }

    public static final ByteBufferAccess forOrder(boolean littleEndian) {
        return littleEndian ? littleEndian() : bigEndian();
    }
}