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Fork of https://github.com/airlift/aircompressor (zstd only). This module is temporary until we get an official release that includes the ZstdInputStream API (which is already implemented by two different people but neither PR shows any progress).

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/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package ai.vespa.airlift.zstd;

import static ai.vespa.airlift.zstd.Constants.SIZE_OF_LONG;
import static ai.vespa.airlift.zstd.UnsafeUtil.UNSAFE;
import static ai.vespa.airlift.zstd.Util.checkArgument;

class BitOutputStream
{
    private static final long[] BIT_MASK = {
            0x0, 0x1, 0x3, 0x7, 0xF, 0x1F,
            0x3F, 0x7F, 0xFF, 0x1FF, 0x3FF, 0x7FF,
            0xFFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF, 0x1FFFF,
            0x3FFFF, 0x7FFFF, 0xFFFFF, 0x1FFFFF, 0x3FFFFF, 0x7FFFFF,
            0xFFFFFF, 0x1FFFFFF, 0x3FFFFFF, 0x7FFFFFF, 0xFFFFFFF, 0x1FFFFFFF,
            0x3FFFFFFF, 0x7FFFFFFF}; // up to 31 bits

    private final Object outputBase;
    private final long outputAddress;
    private final long outputLimit;

    private long container;
    private int bitCount;
    private long currentAddress;

    public BitOutputStream(Object outputBase, long outputAddress, int outputSize)
    {
        checkArgument(outputSize >= SIZE_OF_LONG, "Output buffer too small");

        this.outputBase = outputBase;
        this.outputAddress = outputAddress;
        outputLimit = this.outputAddress + outputSize - SIZE_OF_LONG;

        currentAddress = this.outputAddress;
    }

    public void addBits(int value, int bits)
    {
        container |= (value & BIT_MASK[bits]) << bitCount;
        bitCount += bits;
    }

    /**
     * Note: leading bits of value must be 0
     */
    public void addBitsFast(int value, int bits)
    {
        container |= ((long) value) << bitCount;
        bitCount += bits;
    }

    public void flush()
    {
        int bytes = bitCount >>> 3;

        UNSAFE.putLong(outputBase, currentAddress, container);
        currentAddress += bytes;

        if (currentAddress > outputLimit) {
            currentAddress = outputLimit;
        }

        bitCount &= 7;
        container >>>= bytes * 8;
    }

    public int close()
    {
        addBitsFast(1, 1); // end mark
        flush();

        if (currentAddress >= outputLimit) {
            return 0;
        }

        return (int) ((currentAddress - outputAddress) + (bitCount > 0 ? 1 : 0));
    }
}