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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.highestBit;
import static ai.vespa.airlift.zstd.Util.verify;
/**
* 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.
* <p>
* <p>
* ... [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 BitInputStream
{
private BitInputStream()
{
}
public static boolean isEndOfStream(long startAddress, long currentAddress, int bitsConsumed)
{
return startAddress == currentAddress && bitsConsumed == Long.SIZE;
}
@SuppressWarnings("fallthrough")
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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