/*
 * Copyright (C) 2014 The Android Open Source Project
 * Copyright (c) 2000, 2021, 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.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * 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 java.nio;

import java.security.AccessController;

import sun.misc.VM;
import jdk.internal.access.SharedSecrets;
import jdk.internal.misc.Unsafe;

import java.util.concurrent.atomic.AtomicLong;

/**
 * Access to bits, native and otherwise.
 */

class Bits {                            // package-private

    private Bits() { }


    // -- Swapping --

    static short swap(short x) {
        return Short.reverseBytes(x);
    }

    static char swap(char x) {
        return Character.reverseBytes(x);
    }

    static int swap(int x) {
        return Integer.reverseBytes(x);
    }

    static long swap(long x) {
        return Long.reverseBytes(x);
    }

    // BEGIN Android-added: Getter / Setters needed due to unsupported ScopedMemoryAccess.
    // -- get/put char --

    static private char makeChar(byte b1, byte b0) {
        return (char)((b1 << 8) | (b0 & 0xff));
    }

    static char getCharL(ByteBuffer bb, int bi) {
        return makeChar(bb._get(bi + 1),
                        bb._get(bi    ));
    }

    static char getCharL(long a) {
        return makeChar(_get(a + 1),
                        _get(a    ));
    }

    static char getCharB(ByteBuffer bb, int bi) {
        return makeChar(bb._get(bi    ),
                        bb._get(bi + 1));
    }

    static char getCharB(long a) {
        return makeChar(_get(a    ),
                        _get(a + 1));
    }

    static char getChar(ByteBuffer bb, int bi, boolean bigEndian) {
        return bigEndian ? getCharB(bb, bi) : getCharL(bb, bi);
    }

    static char getChar(long a, boolean bigEndian) {
        return bigEndian ? getCharB(a) : getCharL(a);
    }

    private static byte char1(char x) { return (byte)(x >> 8); }
    private static byte char0(char x) { return (byte)(x     ); }

    static void putCharL(ByteBuffer bb, int bi, char x) {
        bb._put(bi    , char0(x));
        bb._put(bi + 1, char1(x));
    }

    static void putCharL(long a, char x) {
        _put(a    , char0(x));
        _put(a + 1, char1(x));
    }

    static void putCharB(ByteBuffer bb, int bi, char x) {
        bb._put(bi    , char1(x));
        bb._put(bi + 1, char0(x));
    }

    static void putCharB(long a, char x) {
        _put(a    , char1(x));
        _put(a + 1, char0(x));
    }

    static void putChar(ByteBuffer bb, int bi, char x, boolean bigEndian) {
        if (bigEndian)
            putCharB(bb, bi, x);
        else
            putCharL(bb, bi, x);
    }

    static void putChar(long a, char x, boolean bigEndian) {
        if (bigEndian)
            putCharB(a, x);
        else
            putCharL(a, x);
    }


    // -- get/put short --

    static private short makeShort(byte b1, byte b0) {
        return (short)((b1 << 8) | (b0 & 0xff));
    }

    static short getShortL(ByteBuffer bb, int bi) {
        return makeShort(bb._get(bi + 1),
                         bb._get(bi    ));
    }

    static short getShortL(long a) {
        return makeShort(_get(a + 1),
                         _get(a    ));
    }

    static short getShortB(ByteBuffer bb, int bi) {
        return makeShort(bb._get(bi    ),
                         bb._get(bi + 1));
    }

    static short getShortB(long a) {
        return makeShort(_get(a    ),
                         _get(a + 1));
    }

    static short getShort(ByteBuffer bb, int bi, boolean bigEndian) {
        return bigEndian ? getShortB(bb, bi) : getShortL(bb, bi);
    }

    static short getShort(long a, boolean bigEndian) {
        return bigEndian ? getShortB(a) : getShortL(a);
    }

    private static byte short1(short x) { return (byte)(x >> 8); }
    private static byte short0(short x) { return (byte)(x     ); }

    static void putShortL(ByteBuffer bb, int bi, short x) {
        bb._put(bi    , short0(x));
        bb._put(bi + 1, short1(x));
    }

    static void putShortL(long a, short x) {
        _put(a    , short0(x));
        _put(a + 1, short1(x));
    }

    static void putShortB(ByteBuffer bb, int bi, short x) {
        bb._put(bi    , short1(x));
        bb._put(bi + 1, short0(x));
    }

    static void putShortB(long a, short x) {
        _put(a    , short1(x));
        _put(a + 1, short0(x));
    }

    static void putShort(ByteBuffer bb, int bi, short x, boolean bigEndian) {
        if (bigEndian)
            putShortB(bb, bi, x);
        else
            putShortL(bb, bi, x);
    }

    static void putShort(long a, short x, boolean bigEndian) {
        if (bigEndian)
            putShortB(a, x);
        else
            putShortL(a, x);
    }


    // -- get/put int --

    static private int makeInt(byte b3, byte b2, byte b1, byte b0) {
        return (((b3       ) << 24) |
                ((b2 & 0xff) << 16) |
                ((b1 & 0xff) <<  8) |
                ((b0 & 0xff)      ));
    }

    static int getIntL(ByteBuffer bb, int bi) {
        return makeInt(bb._get(bi + 3),
                       bb._get(bi + 2),
                       bb._get(bi + 1),
                       bb._get(bi    ));
    }

    static int getIntL(long a) {
        return makeInt(_get(a + 3),
                       _get(a + 2),
                       _get(a + 1),
                       _get(a    ));
    }

    static int getIntB(ByteBuffer bb, int bi) {
        return makeInt(bb._get(bi    ),
                       bb._get(bi + 1),
                       bb._get(bi + 2),
                       bb._get(bi + 3));
    }

    static int getIntB(long a) {
        return makeInt(_get(a    ),
                       _get(a + 1),
                       _get(a + 2),
                       _get(a + 3));
    }

    static int getInt(ByteBuffer bb, int bi, boolean bigEndian) {
        return bigEndian ? getIntB(bb, bi) : getIntL(bb, bi) ;
    }

    static int getInt(long a, boolean bigEndian) {
        return bigEndian ? getIntB(a) : getIntL(a) ;
    }

    private static byte int3(int x) { return (byte)(x >> 24); }
    private static byte int2(int x) { return (byte)(x >> 16); }
    private static byte int1(int x) { return (byte)(x >>  8); }
    private static byte int0(int x) { return (byte)(x      ); }

    static void putIntL(ByteBuffer bb, int bi, int x) {
        bb._put(bi + 3, int3(x));
        bb._put(bi + 2, int2(x));
        bb._put(bi + 1, int1(x));
        bb._put(bi    , int0(x));
    }

    static void putIntL(long a, int x) {
        _put(a + 3, int3(x));
        _put(a + 2, int2(x));
        _put(a + 1, int1(x));
        _put(a    , int0(x));
    }

    static void putIntB(ByteBuffer bb, int bi, int x) {
        bb._put(bi    , int3(x));
        bb._put(bi + 1, int2(x));
        bb._put(bi + 2, int1(x));
        bb._put(bi + 3, int0(x));
    }

    static void putIntB(long a, int x) {
        _put(a    , int3(x));
        _put(a + 1, int2(x));
        _put(a + 2, int1(x));
        _put(a + 3, int0(x));
    }

    static void putInt(ByteBuffer bb, int bi, int x, boolean bigEndian) {
        if (bigEndian)
            putIntB(bb, bi, x);
        else
            putIntL(bb, bi, x);
    }

    static void putInt(long a, int x, boolean bigEndian) {
        if (bigEndian)
            putIntB(a, x);
        else
            putIntL(a, x);
    }


    // -- get/put long --

    static private long makeLong(byte b7, byte b6, byte b5, byte b4,
                                 byte b3, byte b2, byte b1, byte b0)
    {
        return ((((long)b7       ) << 56) |
                (((long)b6 & 0xff) << 48) |
                (((long)b5 & 0xff) << 40) |
                (((long)b4 & 0xff) << 32) |
                (((long)b3 & 0xff) << 24) |
                (((long)b2 & 0xff) << 16) |
                (((long)b1 & 0xff) <<  8) |
                (((long)b0 & 0xff)      ));
    }

    static long getLongL(ByteBuffer bb, int bi) {
        return makeLong(bb._get(bi + 7),
                        bb._get(bi + 6),
                        bb._get(bi + 5),
                        bb._get(bi + 4),
                        bb._get(bi + 3),
                        bb._get(bi + 2),
                        bb._get(bi + 1),
                        bb._get(bi    ));
    }

    static long getLongL(long a) {
        return makeLong(_get(a + 7),
                        _get(a + 6),
                        _get(a + 5),
                        _get(a + 4),
                        _get(a + 3),
                        _get(a + 2),
                        _get(a + 1),
                        _get(a    ));
    }

    static long getLongB(ByteBuffer bb, int bi) {
        return makeLong(bb._get(bi    ),
                        bb._get(bi + 1),
                        bb._get(bi + 2),
                        bb._get(bi + 3),
                        bb._get(bi + 4),
                        bb._get(bi + 5),
                        bb._get(bi + 6),
                        bb._get(bi + 7));
    }

    static long getLongB(long a) {
        return makeLong(_get(a    ),
                        _get(a + 1),
                        _get(a + 2),
                        _get(a + 3),
                        _get(a + 4),
                        _get(a + 5),
                        _get(a + 6),
                        _get(a + 7));
    }

    static long getLong(ByteBuffer bb, int bi, boolean bigEndian) {
        return bigEndian ? getLongB(bb, bi) : getLongL(bb, bi);
    }

    static long getLong(long a, boolean bigEndian) {
        return bigEndian ? getLongB(a) : getLongL(a);
    }

    private static byte long7(long x) { return (byte)(x >> 56); }
    private static byte long6(long x) { return (byte)(x >> 48); }
    private static byte long5(long x) { return (byte)(x >> 40); }
    private static byte long4(long x) { return (byte)(x >> 32); }
    private static byte long3(long x) { return (byte)(x >> 24); }
    private static byte long2(long x) { return (byte)(x >> 16); }
    private static byte long1(long x) { return (byte)(x >>  8); }
    private static byte long0(long x) { return (byte)(x      ); }

    static void putLongL(ByteBuffer bb, int bi, long x) {
        bb._put(bi + 7, long7(x));
        bb._put(bi + 6, long6(x));
        bb._put(bi + 5, long5(x));
        bb._put(bi + 4, long4(x));
        bb._put(bi + 3, long3(x));
        bb._put(bi + 2, long2(x));
        bb._put(bi + 1, long1(x));
        bb._put(bi    , long0(x));
    }

    static void putLongL(long a, long x) {
        _put(a + 7, long7(x));
        _put(a + 6, long6(x));
        _put(a + 5, long5(x));
        _put(a + 4, long4(x));
        _put(a + 3, long3(x));
        _put(a + 2, long2(x));
        _put(a + 1, long1(x));
        _put(a    , long0(x));
    }

    static void putLongB(ByteBuffer bb, int bi, long x) {
        bb._put(bi    , long7(x));
        bb._put(bi + 1, long6(x));
        bb._put(bi + 2, long5(x));
        bb._put(bi + 3, long4(x));
        bb._put(bi + 4, long3(x));
        bb._put(bi + 5, long2(x));
        bb._put(bi + 6, long1(x));
        bb._put(bi + 7, long0(x));
    }

    static void putLongB(long a, long x) {
        _put(a    , long7(x));
        _put(a + 1, long6(x));
        _put(a + 2, long5(x));
        _put(a + 3, long4(x));
        _put(a + 4, long3(x));
        _put(a + 5, long2(x));
        _put(a + 6, long1(x));
        _put(a + 7, long0(x));
    }

    static void putLong(ByteBuffer bb, int bi, long x, boolean bigEndian) {
        if (bigEndian)
            putLongB(bb, bi, x);
        else
            putLongL(bb, bi, x);
    }

    static void putLong(long a, long x, boolean bigEndian) {
        if (bigEndian)
            putLongB(a, x);
        else
            putLongL(a, x);
    }


    // -- get/put float --

    static float getFloatL(ByteBuffer bb, int bi) {
        return Float.intBitsToFloat(getIntL(bb, bi));
    }

    static float getFloatL(long a) {
        return Float.intBitsToFloat(getIntL(a));
    }

    static float getFloatB(ByteBuffer bb, int bi) {
        return Float.intBitsToFloat(getIntB(bb, bi));
    }

    static float getFloatB(long a) {
        return Float.intBitsToFloat(getIntB(a));
    }

    static float getFloat(ByteBuffer bb, int bi, boolean bigEndian) {
        return bigEndian ? getFloatB(bb, bi) : getFloatL(bb, bi);
    }

    static float getFloat(long a, boolean bigEndian) {
        return bigEndian ? getFloatB(a) : getFloatL(a);
    }

    static void putFloatL(ByteBuffer bb, int bi, float x) {
        putIntL(bb, bi, Float.floatToRawIntBits(x));
    }

    static void putFloatL(long a, float x) {
        putIntL(a, Float.floatToRawIntBits(x));
    }

    static void putFloatB(ByteBuffer bb, int bi, float x) {
        putIntB(bb, bi, Float.floatToRawIntBits(x));
    }

    static void putFloatB(long a, float x) {
        putIntB(a, Float.floatToRawIntBits(x));
    }

    static void putFloat(ByteBuffer bb, int bi, float x, boolean bigEndian) {
        if (bigEndian)
            putFloatB(bb, bi, x);
        else
            putFloatL(bb, bi, x);
    }

    static void putFloat(long a, float x, boolean bigEndian) {
        if (bigEndian)
            putFloatB(a, x);
        else
            putFloatL(a, x);
    }


    // -- get/put double --

    static double getDoubleL(ByteBuffer bb, int bi) {
        return Double.longBitsToDouble(getLongL(bb, bi));
    }

    static double getDoubleL(long a) {
        return Double.longBitsToDouble(getLongL(a));
    }

    static double getDoubleB(ByteBuffer bb, int bi) {
        return Double.longBitsToDouble(getLongB(bb, bi));
    }

    static double getDoubleB(long a) {
        return Double.longBitsToDouble(getLongB(a));
    }

    static double getDouble(ByteBuffer bb, int bi, boolean bigEndian) {
        return bigEndian ? getDoubleB(bb, bi) : getDoubleL(bb, bi);
    }

    static double getDouble(long a, boolean bigEndian) {
        return bigEndian ? getDoubleB(a) : getDoubleL(a);
    }

    static void putDoubleL(ByteBuffer bb, int bi, double x) {
        putLongL(bb, bi, Double.doubleToRawLongBits(x));
    }

    static void putDoubleL(long a, double x) {
        putLongL(a, Double.doubleToRawLongBits(x));
    }

    static void putDoubleB(ByteBuffer bb, int bi, double x) {
        putLongB(bb, bi, Double.doubleToRawLongBits(x));
    }

    static void putDoubleB(long a, double x) {
        putLongB(a, Double.doubleToRawLongBits(x));
    }

    static void putDouble(ByteBuffer bb, int bi, double x, boolean bigEndian) {
        if (bigEndian)
            putDoubleB(bb, bi, x);
        else
            putDoubleL(bb, bi, x);
    }

    static void putDouble(long a, double x, boolean bigEndian) {
        if (bigEndian)
            putDoubleB(a, x);
        else
            putDoubleL(a, x);
    }

    private static byte _get(long a) {
        return UNSAFE.getByte(a);
    }

    private static void _put(long a, byte b) {
        UNSAFE.putByte(a, b);
    }
    // END Android-added: Getter / Setters needed due to unsupported ScopedMemoryAccess.

    // -- Unsafe access --

    private static final Unsafe UNSAFE = Unsafe.getUnsafe();

    // -- Processor and memory-system properties --

    private static int PAGE_SIZE = -1;

    static int pageSize() {
        if (PAGE_SIZE == -1)
            PAGE_SIZE = UNSAFE.pageSize();
        return PAGE_SIZE;
    }

    static long pageCount(long size) {
        return (size + (long)pageSize() - 1L) / pageSize();
    }
    // Android-removed: Remove unused methods.
    /*
    private static boolean UNALIGNED = UNSAFE.unalignedAccess();

    static boolean unaligned() {
        return UNALIGNED;
    }
    */


    // -- Direct memory management --

    // BEGIN Android-removed: Direct memory management unused on Android.
    /*
    // A user-settable upper limit on the maximum amount of allocatable
    // direct buffer memory.  This value may be changed during VM
    // initialization if it is launched with "-XX:MaxDirectMemorySize=<size>".
    private static volatile long MAX_MEMORY = VM.maxDirectMemory();
    private static final AtomicLong RESERVED_MEMORY = new AtomicLong();
    private static final AtomicLong TOTAL_CAPACITY = new AtomicLong();
    private static final AtomicLong COUNT = new AtomicLong();
    private static volatile boolean MEMORY_LIMIT_SET;

    // max. number of sleeps during try-reserving with exponentially
    // increasing delay before throwing OutOfMemoryError:
    // 1, 2, 4, 8, 16, 32, 64, 128, 256 (total 511 ms ~ 0.5 s)
    // which means that OOME will be thrown after 0.5 s of trying
    private static final int MAX_SLEEPS = 9;

    // These methods should be called whenever direct memory is allocated or
    // freed.  They allow the user to control the amount of direct memory
    // which a process may access.  All sizes are specified in bytes.
    static void reserveMemory(long size, long cap) {

        if (!MEMORY_LIMIT_SET && VM.initLevel() >= 1) {
            MAX_MEMORY = VM.maxDirectMemory();
            MEMORY_LIMIT_SET = true;
        }

        // optimist!
        if (tryReserveMemory(size, cap)) {
            return;
        }

        final JavaLangRefAccess jlra = SharedSecrets.getJavaLangRefAccess();
        boolean interrupted = false;
        try {

            // Retry allocation until success or there are no more
            // references (including Cleaners that might free direct
            // buffer memory) to process and allocation still fails.
            boolean refprocActive;
            do {
                try {
                    refprocActive = jlra.waitForReferenceProcessing();
                } catch (InterruptedException e) {
                    // Defer interrupts and keep trying.
                    interrupted = true;
                    refprocActive = true;
                }
                if (tryReserveMemory(size, cap)) {
                    return;
                }
            } while (refprocActive);

            // trigger VM's Reference processing
            System.gc();

            // A retry loop with exponential back-off delays.
            // Sometimes it would suffice to give up once reference
            // processing is complete.  But if there are many threads
            // competing for memory, this gives more opportunities for
            // any given thread to make progress.  In particular, this
            // seems to be enough for a stress test like
            // DirectBufferAllocTest to (usually) succeed, while
            // without it that test likely fails.  Since failure here
            // ends in OOME, there's no need to hurry.
            long sleepTime = 1;
            int sleeps = 0;
            while (true) {
                if (tryReserveMemory(size, cap)) {
                    return;
                }
                if (sleeps >= MAX_SLEEPS) {
                    break;
                }
                try {
                    if (!jlra.waitForReferenceProcessing()) {
                        Thread.sleep(sleepTime);
                        sleepTime <<= 1;
                        sleeps++;
                    }
                } catch (InterruptedException e) {
                    interrupted = true;
                }
            }

            // no luck
            throw new OutOfMemoryError
                ("Cannot reserve "
                 + size + " bytes of direct buffer memory (allocated: "
                 + RESERVED_MEMORY.get() + ", limit: " + MAX_MEMORY +")");

        } finally {
            if (interrupted) {
                // don't swallow interrupts
                Thread.currentThread().interrupt();
            }
        }
    }

    private static boolean tryReserveMemory(long size, long cap) {

        // -XX:MaxDirectMemorySize limits the total capacity rather than the
        // actual memory usage, which will differ when buffers are page
        // aligned.
        long totalCap;
        while (cap <= MAX_MEMORY - (totalCap = TOTAL_CAPACITY.get())) {
            if (TOTAL_CAPACITY.compareAndSet(totalCap, totalCap + cap)) {
                RESERVED_MEMORY.addAndGet(size);
                COUNT.incrementAndGet();
                return true;
            }
        }

        return false;
    }


    static void unreserveMemory(long size, long cap) {
        long cnt = COUNT.decrementAndGet();
        long reservedMem = RESERVED_MEMORY.addAndGet(-size);
        long totalCap = TOTAL_CAPACITY.addAndGet(-cap);
        assert cnt >= 0 && reservedMem >= 0 && totalCap >= 0;
    }

    static final BufferPool BUFFER_POOL = new BufferPool() {
        @Override
        public String getName() {
            return "direct";
        }
        @Override
        public long getCount() {
            return Bits.COUNT.get();
        }
        @Override
        public long getTotalCapacity() {
            return Bits.TOTAL_CAPACITY.get();
        }
        @Override
        public long getMemoryUsed() {
            return Bits.RESERVED_MEMORY.get();
        }
    };

    // These numbers represent the point at which we have empirically
    // determined that the average cost of a JNI call exceeds the expense
    // of an element by element copy.  These numbers may change over time.
    static final int JNI_COPY_TO_ARRAY_THRESHOLD   = 6;
    static final int JNI_COPY_FROM_ARRAY_THRESHOLD = 6;
    */
    // END Android-removed: Direct memory management unused on Android.
}