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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 io.airlift.compress.zstd;

import static io.airlift.compress.zstd.UnsafeUtil.UNSAFE;
import static io.airlift.compress.zstd.Util.highestBit;
import static io.airlift.compress.zstd.Util.verify;
import static io.airlift.compress.zstd.ZstdFrameDecompressor.SIZE_OF_LONG;

/**
 * Bit streams are encoded as a byte-aligned little-endian stream. Thus, bits are laid out
 * in the following manner, and the stream is read from right to left.
 * 

*

* ... [16 17 18 19 20 21 22 23] [8 9 10 11 12 13 14 15] [0 1 2 3 4 5 6 7] */ class BitStream { private BitStream() { } public static boolean isEndOfStream(long startAddress, long currentAddress, int bitsConsumed) { return startAddress == currentAddress && bitsConsumed == Long.SIZE; } static long readTail(Object inputBase, long inputAddress, int inputSize) { long bits = UNSAFE.getByte(inputBase, inputAddress) & 0xFF; switch (inputSize) { case 7: bits |= (UNSAFE.getByte(inputBase, inputAddress + 6) & 0xFFL) << 48; case 6: bits |= (UNSAFE.getByte(inputBase, inputAddress + 5) & 0xFFL) << 40; case 5: bits |= (UNSAFE.getByte(inputBase, inputAddress + 4) & 0xFFL) << 32; case 4: bits |= (UNSAFE.getByte(inputBase, inputAddress + 3) & 0xFFL) << 24; case 3: bits |= (UNSAFE.getByte(inputBase, inputAddress + 2) & 0xFFL) << 16; case 2: bits |= (UNSAFE.getByte(inputBase, inputAddress + 1) & 0xFFL) << 8; } return bits; } /** * @return numberOfBits in the low order bits of a long */ public static long peekBits(int bitsConsumed, long bitContainer, int numberOfBits) { return (((bitContainer << bitsConsumed) >>> 1) >>> (63 - numberOfBits)); } /** * numberOfBits must be > 0 * * @return numberOfBits in the low order bits of a long */ public static long peekBitsFast(int bitsConsumed, long bitContainer, int numberOfBits) { return ((bitContainer << bitsConsumed) >>> (64 - numberOfBits)); } static class Initializer { private final Object inputBase; private final long startAddress; private final long endAddress; private long bits; private long currentAddress; private int bitsConsumed; public Initializer(Object inputBase, long startAddress, long endAddress) { this.inputBase = inputBase; this.startAddress = startAddress; this.endAddress = endAddress; } public long getBits() { return bits; } public long getCurrentAddress() { return currentAddress; } public int getBitsConsumed() { return bitsConsumed; } public void initialize() { verify(endAddress - startAddress >= 1, startAddress, "Bitstream is empty"); int lastByte = UNSAFE.getByte(inputBase, endAddress - 1) & 0xFF; verify(lastByte != 0, endAddress, "Bitstream end mark not present"); bitsConsumed = SIZE_OF_LONG - highestBit(lastByte); int inputSize = (int) (endAddress - startAddress); if (inputSize >= SIZE_OF_LONG) { /* normal case */ currentAddress = endAddress - SIZE_OF_LONG; bits = UNSAFE.getLong(inputBase, currentAddress); } else { currentAddress = startAddress; bits = readTail(inputBase, startAddress, inputSize); bitsConsumed += (SIZE_OF_LONG - inputSize) * 8; } } } static final class Loader { private final Object inputBase; private final long startAddress; private long bits; private long currentAddress; private int bitsConsumed; private boolean overflow; public Loader(Object inputBase, long startAddress, long currentAddress, long bits, int bitsConsumed) { this.inputBase = inputBase; this.startAddress = startAddress; this.bits = bits; this.currentAddress = currentAddress; this.bitsConsumed = bitsConsumed; } public long getBits() { return bits; } public long getCurrentAddress() { return currentAddress; } public int getBitsConsumed() { return bitsConsumed; } public boolean isOverflow() { return overflow; } public boolean load() { if (bitsConsumed > 64) { overflow = true; return true; } else if (currentAddress == startAddress) { return true; } int bytes = bitsConsumed >>> 3; // divide by 8 if (currentAddress >= startAddress + SIZE_OF_LONG) { if (bytes > 0) { currentAddress -= bytes; bits = UNSAFE.getLong(inputBase, currentAddress); } bitsConsumed &= 0b111; } else if (currentAddress - bytes < startAddress) { bytes = (int) (currentAddress - startAddress); currentAddress = startAddress; bitsConsumed -= bytes * SIZE_OF_LONG; bits = UNSAFE.getLong(inputBase, startAddress); return true; } else { currentAddress -= bytes; bitsConsumed -= bytes * SIZE_OF_LONG; bits = UNSAFE.getLong(inputBase, currentAddress); } return false; } } }





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