org.apache.lucene.util.packed.XPackedInts Maven / Gradle / Ivy
Show all versions of opensearch Show documentation
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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 org.apache.lucene.util.packed;
import org.apache.lucene.codecs.CodecUtil;
import org.apache.lucene.store.DataInput;
import org.apache.lucene.store.DataOutput;
import org.apache.lucene.store.IndexInput;
import org.apache.lucene.util.RamUsageEstimator;
import org.apache.lucene.util.packed.PackedInts.Decoder;
import org.apache.lucene.util.packed.PackedInts.Encoder;
import org.apache.lucene.util.packed.PackedInts.Format;
import org.apache.lucene.util.packed.PackedInts.FormatAndBits;
import org.apache.lucene.util.packed.PackedInts.Reader;
import org.apache.lucene.util.packed.PackedInts.ReaderIterator;
import org.apache.lucene.util.packed.PackedInts.Writer;
import java.io.EOFException;
import java.io.IOException;
import java.util.Arrays;
/**
* Forked from Lucene 8.x; removed in Lucene 8.9
*
* Todo: further investigate a better alternative
*
* Simplistic compression for array of unsigned long values. Each value is {@code >= 0} and {@code
* <=} a specified maximum value. The values are stored as packed ints, with each value consuming a
* fixed number of bits.
*/
public class XPackedInts {
/** At most 700% memory overhead, always select a direct implementation. */
public static final float FASTEST = 7f;
/** At most 50% memory overhead, always select a reasonably fast implementation. */
public static final float FAST = 0.5f;
/** At most 25% memory overhead. */
public static final float DEFAULT = 0.25f;
/** No memory overhead at all, but the returned implementation may be slow. */
public static final float COMPACT = 0f;
/** Default amount of memory to use for bulk operations. */
public static final int DEFAULT_BUFFER_SIZE = 1024; // 1K
public static final String CODEC_NAME = "PackedInts";
public static final int VERSION_MONOTONIC_WITHOUT_ZIGZAG = 2;
public static final int VERSION_START = VERSION_MONOTONIC_WITHOUT_ZIGZAG;
public static final int VERSION_CURRENT = VERSION_MONOTONIC_WITHOUT_ZIGZAG;
/** Check the validity of a version number. */
public static void checkVersion(int version) {
if (version < VERSION_START) {
throw new IllegalArgumentException("Version is too old, should be at least " + VERSION_START + " (got " + version + ")");
} else if (version > VERSION_CURRENT) {
throw new IllegalArgumentException("Version is too new, should be at most " + VERSION_CURRENT + " (got " + version + ")");
}
}
/**
* Try to find the {@link Format} and number of bits per value that would restore from disk the
* fastest reader whose overhead is less than acceptableOverheadRatio.
*
*
The acceptableOverheadRatio parameter makes sense for random-access {@link
* Reader}s. In case you only plan to perform sequential access on this stream later on, you
* should probably use {@link PackedInts#COMPACT}.
*
*
If you don't know how many values you are going to write, use valueCount = -1.
*/
public static FormatAndBits fastestFormatAndBits(int valueCount, int bitsPerValue, float acceptableOverheadRatio) {
if (valueCount == -1) {
valueCount = Integer.MAX_VALUE;
}
acceptableOverheadRatio = Math.max(COMPACT, acceptableOverheadRatio);
acceptableOverheadRatio = Math.min(FASTEST, acceptableOverheadRatio);
float acceptableOverheadPerValue = acceptableOverheadRatio * bitsPerValue; // in bits
int maxBitsPerValue = bitsPerValue + (int) acceptableOverheadPerValue;
int actualBitsPerValue = -1;
// rounded number of bits per value are usually the fastest
if (bitsPerValue <= 8 && maxBitsPerValue >= 8) {
actualBitsPerValue = 8;
} else if (bitsPerValue <= 16 && maxBitsPerValue >= 16) {
actualBitsPerValue = 16;
} else if (bitsPerValue <= 32 && maxBitsPerValue >= 32) {
actualBitsPerValue = 32;
} else if (bitsPerValue <= 64 && maxBitsPerValue >= 64) {
actualBitsPerValue = 64;
} else {
actualBitsPerValue = bitsPerValue;
}
return new FormatAndBits(Format.PACKED, actualBitsPerValue);
}
final static class XPackedWriter extends XWriter {
boolean finished;
final PackedInts.Format format;
final BulkOperation encoder;
final byte[] nextBlocks;
final long[] nextValues;
final int iterations;
int off;
int written;
XPackedWriter(PackedInts.Format format, DataOutput out, int valueCount, int bitsPerValue, int mem) {
super(out, valueCount, bitsPerValue);
this.format = format;
encoder = BulkOperation.of(format, bitsPerValue);
iterations = encoder.computeIterations(valueCount, mem);
nextBlocks = new byte[iterations * encoder.byteBlockCount()];
nextValues = new long[iterations * encoder.byteValueCount()];
off = 0;
written = 0;
finished = false;
}
@Override
protected PackedInts.Format getFormat() {
return format;
}
@Override
public void add(long v) throws IOException {
assert PackedInts.unsignedBitsRequired(v) <= bitsPerValue;
assert !finished;
if (valueCount != -1 && written >= valueCount) {
throw new EOFException("Writing past end of stream");
}
nextValues[off++] = v;
if (off == nextValues.length) {
flush();
}
++written;
}
@Override
public void finish() throws IOException {
assert !finished;
if (valueCount != -1) {
while (written < valueCount) {
add(0L);
}
}
flush();
finished = true;
}
private void flush() throws IOException {
encoder.encode(nextValues, 0, nextBlocks, 0, iterations);
final int blockCount = (int) format.byteCount(PackedInts.VERSION_CURRENT, off, bitsPerValue);
out.writeBytes(nextBlocks, blockCount);
Arrays.fill(nextValues, 0L);
off = 0;
}
@Override
public int ord() {
return written - 1;
}
}
/**
* A packed integer array that can be modified.
*
*/
public abstract static class Mutable extends Reader {
/**
* @return the number of bits used to store any given value. Note: This does not imply that
* memory usage is {@code bitsPerValue * #values} as implementations are free to use
* non-space-optimal packing of bits.
*/
public abstract int getBitsPerValue();
/**
* Set the value at the given index in the array.
*
* @param index where the value should be positioned.
* @param value a value conforming to the constraints set by the array.
*/
public abstract void set(int index, long value);
/**
* Bulk set: set at least one and at most len longs starting at off in
* arr into this mutable, starting at index. Returns the actual number
* of values that have been set.
*/
public int set(int index, long[] arr, int off, int len) {
assert len > 0 : "len must be > 0 (got " + len + ")";
assert index >= 0 && index < size();
len = Math.min(len, size() - index);
assert off + len <= arr.length;
for (int i = index, o = off, end = index + len; i < end; ++i, ++o) {
set(i, arr[o]);
}
return len;
}
/**
* Fill the mutable from fromIndex (inclusive) to toIndex (exclusive)
* with val.
*/
public void fill(int fromIndex, int toIndex, long val) {
assert val <= maxValue(getBitsPerValue());
assert fromIndex <= toIndex;
for (int i = fromIndex; i < toIndex; ++i) {
set(i, val);
}
}
/** Sets all values to 0. */
public void clear() {
fill(0, size(), 0);
}
/**
* Save this mutable into out. Instantiating a reader from the generated data will
* return a reader with the same number of bits per value.
*/
public void save(DataOutput out) throws IOException {
XWriter writer = getWriterNoHeader(out, getFormat(), size(), getBitsPerValue(), DEFAULT_BUFFER_SIZE);
writer.writeHeader();
for (int i = 0; i < size(); ++i) {
writer.add(get(i));
}
writer.finish();
}
/** The underlying format. */
Format getFormat() {
return Format.PACKED;
}
}
/**
* A simple base for Readers that keeps track of valueCount and bitsPerValue.
*
*/
abstract static class ReaderImpl extends Reader {
protected final int valueCount;
protected ReaderImpl(int valueCount) {
this.valueCount = valueCount;
}
@Override
public abstract long get(int index);
@Override
public final int size() {
return valueCount;
}
}
abstract static class MutableImpl extends Mutable {
protected final int valueCount;
protected final int bitsPerValue;
protected MutableImpl(int valueCount, int bitsPerValue) {
this.valueCount = valueCount;
assert bitsPerValue > 0 && bitsPerValue <= 64 : "bitsPerValue=" + bitsPerValue;
this.bitsPerValue = bitsPerValue;
}
@Override
public final int getBitsPerValue() {
return bitsPerValue;
}
@Override
public final int size() {
return valueCount;
}
@Override
public String toString() {
return getClass().getSimpleName() + "(valueCount=" + valueCount + ",bitsPerValue=" + bitsPerValue + ")";
}
}
/** A {@link Reader} which has all its values equal to 0 (bitsPerValue = 0). */
public static final class NullReader extends Reader {
private final int valueCount;
/** Sole constructor. */
public NullReader(int valueCount) {
this.valueCount = valueCount;
}
@Override
public long get(int index) {
return 0;
}
@Override
public int get(int index, long[] arr, int off, int len) {
assert len > 0 : "len must be > 0 (got " + len + ")";
assert index >= 0 && index < valueCount;
len = Math.min(len, valueCount - index);
Arrays.fill(arr, off, off + len, 0);
return len;
}
@Override
public int size() {
return valueCount;
}
@Override
public long ramBytesUsed() {
return RamUsageEstimator.alignObjectSize(RamUsageEstimator.NUM_BYTES_OBJECT_HEADER + Integer.BYTES);
}
}
/**
* A write-once Writer.
*
*/
public abstract static class XWriter extends Writer {
protected XWriter(DataOutput out, int valueCount, int bitsPerValue) {
super(out, valueCount, bitsPerValue);
}
void writeHeader() throws IOException {
assert valueCount != -1;
CodecUtil.writeHeader(out, CODEC_NAME, VERSION_CURRENT);
out.writeVInt(bitsPerValue);
out.writeVInt(valueCount);
out.writeVInt(getFormat().getId());
}
}
/**
* Get a {@link Decoder}.
*
* @param format the format used to store packed ints
* @param version the compatibility version
* @param bitsPerValue the number of bits per value
* @return a decoder
*/
public static Decoder getDecoder(Format format, int version, int bitsPerValue) {
checkVersion(version);
return BulkOperation.of(format, bitsPerValue);
}
/**
* Get an {@link Encoder}.
*
* @param format the format used to store packed ints
* @param version the compatibility version
* @param bitsPerValue the number of bits per value
* @return an encoder
*/
public static Encoder getEncoder(Format format, int version, int bitsPerValue) {
checkVersion(version);
return BulkOperation.of(format, bitsPerValue);
}
/**
* Expert: Restore a {@link Reader} from a stream without reading metadata at the beginning of the
* stream. This method is useful to restore data from streams which have been created using {@link
* XPackedInts#getWriterNoHeader(DataOutput, Format, int, int, int)}.
*
* @param in the stream to read data from, positioned at the beginning of the packed values
* @param format the format used to serialize
* @param version the version used to serialize the data
* @param valueCount how many values the stream holds
* @param bitsPerValue the number of bits per value
* @return a Reader
* @throws IOException If there is a low-level I/O error
* @see XPackedInts#getWriterNoHeader(DataOutput, Format, int, int, int)
*/
public static Reader getReaderNoHeader(DataInput in, Format format, int version, int valueCount, int bitsPerValue) throws IOException {
checkVersion(version);
switch (format) {
case PACKED_SINGLE_BLOCK:
return XPacked64SingleBlock.create(in, valueCount, bitsPerValue);
case PACKED:
return new XPacked64(version, in, valueCount, bitsPerValue);
default:
throw new AssertionError("Unknown Writer format: " + format);
}
}
/**
* Restore a {@link Reader} from a stream.
*
* @param in the stream to read data from
* @return a Reader
* @throws IOException If there is a low-level I/O error
*/
public static Reader getReader(DataInput in) throws IOException {
final int version = CodecUtil.checkHeader(in, CODEC_NAME, VERSION_START, VERSION_CURRENT);
final int bitsPerValue = in.readVInt();
assert bitsPerValue > 0 && bitsPerValue <= 64 : "bitsPerValue=" + bitsPerValue;
final int valueCount = in.readVInt();
final Format format = Format.byId(in.readVInt());
return getReaderNoHeader(in, format, version, valueCount, bitsPerValue);
}
/**
* Expert: Restore a {@link ReaderIterator} from a stream without reading metadata at the
* beginning of the stream. This method is useful to restore data from streams which have been
* created using {@link XPackedInts#getWriterNoHeader(DataOutput, Format, int, int, int)}.
*
* @param in the stream to read data from, positioned at the beginning of the packed values
* @param format the format used to serialize
* @param version the version used to serialize the data
* @param valueCount how many values the stream holds
* @param bitsPerValue the number of bits per value
* @param mem how much memory the iterator is allowed to use to read-ahead (likely to speed up
* iteration)
* @return a ReaderIterator
* @see XPackedInts#getWriterNoHeader(DataOutput, Format, int, int, int)
*/
public static ReaderIterator getReaderIteratorNoHeader(
DataInput in,
Format format,
int version,
int valueCount,
int bitsPerValue,
int mem
) {
checkVersion(version);
return new PackedReaderIterator(format, version, valueCount, bitsPerValue, in, mem);
}
/**
* Retrieve PackedInts as a {@link ReaderIterator}
*
* @param in positioned at the beginning of a stored packed int structure.
* @param mem how much memory the iterator is allowed to use to read-ahead (likely to speed up
* iteration)
* @return an iterator to access the values
* @throws IOException if the structure could not be retrieved.
*/
public static ReaderIterator getReaderIterator(DataInput in, int mem) throws IOException {
final int version = CodecUtil.checkHeader(in, CODEC_NAME, VERSION_START, VERSION_CURRENT);
final int bitsPerValue = in.readVInt();
assert bitsPerValue > 0 && bitsPerValue <= 64 : "bitsPerValue=" + bitsPerValue;
final int valueCount = in.readVInt();
final Format format = Format.byId(in.readVInt());
return getReaderIteratorNoHeader(in, format, version, valueCount, bitsPerValue, mem);
}
/**
* Expert: Construct a direct {@link Reader} from a stream without reading metadata at the
* beginning of the stream. This method is useful to restore data from streams which have been
* created using {@link XPackedInts#getWriterNoHeader(DataOutput, Format, int, int, int)}.
*
*
The returned reader will have very little memory overhead, but every call to {@link
* Reader#get(int)} is likely to perform a disk seek.
*
* @param in the stream to read data from
* @param format the format used to serialize
* @param version the version used to serialize the data
* @param valueCount how many values the stream holds
* @param bitsPerValue the number of bits per value
* @return a direct Reader
*/
public static Reader getDirectReaderNoHeader(final IndexInput in, Format format, int version, int valueCount, int bitsPerValue) {
checkVersion(version);
switch (format) {
case PACKED:
return new DirectPackedReader(bitsPerValue, valueCount, in);
case PACKED_SINGLE_BLOCK:
return new DirectPacked64SingleBlockReader(bitsPerValue, valueCount, in);
default:
throw new AssertionError("Unknown format: " + format);
}
}
/**
* Construct a direct {@link Reader} from an {@link IndexInput}. This method is useful to restore
* data from streams which have been created using {@link XPackedInts#getWriter(DataOutput, int,
* int, float)}.
*
*
The returned reader will have very little memory overhead, but every call to {@link
* Reader#get(int)} is likely to perform a disk seek.
*
* @param in the stream to read data from
* @return a direct Reader
* @throws IOException If there is a low-level I/O error
*/
public static Reader getDirectReader(IndexInput in) throws IOException {
final int version = CodecUtil.checkHeader(in, CODEC_NAME, VERSION_START, VERSION_CURRENT);
final int bitsPerValue = in.readVInt();
assert bitsPerValue > 0 && bitsPerValue <= 64 : "bitsPerValue=" + bitsPerValue;
final int valueCount = in.readVInt();
final Format format = Format.byId(in.readVInt());
return getDirectReaderNoHeader(in, format, version, valueCount, bitsPerValue);
}
/**
* Create a packed integer array with the given amount of values initialized to 0. the valueCount
* and the bitsPerValue cannot be changed after creation. All Mutables known by this factory are
* kept fully in RAM.
*
*
Positive values of acceptableOverheadRatio will trade space for speed by
* selecting a faster but potentially less memory-efficient implementation. An
* acceptableOverheadRatio of {@link PackedInts#COMPACT} will make sure that the most
* memory-efficient implementation is selected whereas {@link PackedInts#FASTEST} will make sure
* that the fastest implementation is selected.
*
* @param valueCount the number of elements
* @param bitsPerValue the number of bits available for any given value
* @param acceptableOverheadRatio an acceptable overhead ratio per value
* @return a mutable packed integer array
*/
public static Mutable getMutable(int valueCount, int bitsPerValue, float acceptableOverheadRatio) {
final FormatAndBits formatAndBits = fastestFormatAndBits(valueCount, bitsPerValue, acceptableOverheadRatio);
return getMutable(valueCount, formatAndBits.bitsPerValue, formatAndBits.format);
}
/**
* Same as {@link #getMutable(int, int, float)} with a pre-computed number of bits per value and
* format.
*
*/
public static Mutable getMutable(int valueCount, int bitsPerValue, PackedInts.Format format) {
assert valueCount >= 0;
switch (format) {
case PACKED_SINGLE_BLOCK:
return XPacked64SingleBlock.create(valueCount, bitsPerValue);
case PACKED:
return new XPacked64(valueCount, bitsPerValue);
default:
throw new AssertionError();
}
}
/**
* Expert: Create a packed integer array writer for the given output, format, value count, and
* number of bits per value.
*
*
The resulting stream will be long-aligned. This means that depending on the format which is
* used, up to 63 bits will be wasted. An easy way to make sure that no space is lost is to always
* use a valueCount that is a multiple of 64.
*
*
This method does not write any metadata to the stream, meaning that it is your
* responsibility to store it somewhere else in order to be able to recover data from the stream
* later on:
*
*
* format (using {@link Format#getId()}),
* valueCount,
* bitsPerValue,
* - {@link #VERSION_CURRENT}.
*
*
* It is possible to start writing values without knowing how many of them you are actually
* going to write. To do this, just pass -1 as valueCount. On the other
* hand, for any positive value of valueCount, the returned writer will make sure
* that you don't write more values than expected and pad the end of stream with zeros in case you
* have written less than valueCount when calling {@link Writer#finish()}.
*
*
The mem parameter lets you control how much memory can be used to buffer
* changes in memory before flushing to disk. High values of mem are likely to
* improve throughput. On the other hand, if speed is not that important to you, a value of
* 0 will use as little memory as possible and should already offer reasonable throughput.
*
* @param out the data output
* @param format the format to use to serialize the values
* @param valueCount the number of values
* @param bitsPerValue the number of bits per value
* @param mem how much memory (in bytes) can be used to speed up serialization
* @return a Writer
* @see XPackedInts#getReaderIteratorNoHeader(DataInput, Format, int, int, int, int)
* @see XPackedInts#getReaderNoHeader(DataInput, Format, int, int, int)
*/
public static XWriter getWriterNoHeader(DataOutput out, Format format, int valueCount, int bitsPerValue, int mem) {
return new XPackedWriter(format, out, valueCount, bitsPerValue, mem);
}
/**
* Create a packed integer array writer for the given output, format, value count, and number of
* bits per value.
*
*
The resulting stream will be long-aligned. This means that depending on the format which is
* used under the hoods, up to 63 bits will be wasted. An easy way to make sure that no space is
* lost is to always use a valueCount that is a multiple of 64.
*
*
This method writes metadata to the stream, so that the resulting stream is sufficient to
* restore a {@link Reader} from it. You don't need to track valueCount or
* bitsPerValue by yourself. In case this is a problem, you should probably look at {@link
* #getWriterNoHeader(DataOutput, Format, int, int, int)}.
*
*
The acceptableOverheadRatio parameter controls how readers that will be
* restored from this stream trade space for speed by selecting a faster but potentially less
* memory-efficient implementation. An acceptableOverheadRatio of {@link
* PackedInts#COMPACT} will make sure that the most memory-efficient implementation is selected
* whereas {@link PackedInts#FASTEST} will make sure that the fastest implementation is selected.
* In case you are only interested in reading this stream sequentially later on, you should
* probably use {@link PackedInts#COMPACT}.
*
* @param out the data output
* @param valueCount the number of values
* @param bitsPerValue the number of bits per value
* @param acceptableOverheadRatio an acceptable overhead ratio per value
* @return a Writer
* @throws IOException If there is a low-level I/O error
*/
public static Writer getWriter(DataOutput out, int valueCount, int bitsPerValue, float acceptableOverheadRatio) throws IOException {
assert valueCount >= 0;
final FormatAndBits formatAndBits = fastestFormatAndBits(valueCount, bitsPerValue, acceptableOverheadRatio);
final XWriter writer = getWriterNoHeader(out, formatAndBits.format, valueCount, formatAndBits.bitsPerValue, DEFAULT_BUFFER_SIZE);
writer.writeHeader();
return writer;
}
/**
* Returns how many bits are required to hold values up to and including maxValue NOTE: This
* method returns at least 1.
*
* @param maxValue the maximum value that should be representable.
* @return the amount of bits needed to represent values from 0 to maxValue.
*/
public static int bitsRequired(long maxValue) {
if (maxValue < 0) {
throw new IllegalArgumentException("maxValue must be non-negative (got: " + maxValue + ")");
}
return unsignedBitsRequired(maxValue);
}
/**
* Returns how many bits are required to store bits, interpreted as an unsigned
* value. NOTE: This method returns at least 1.
*
*/
public static int unsignedBitsRequired(long bits) {
return Math.max(1, 64 - Long.numberOfLeadingZeros(bits));
}
/**
* Calculates the maximum unsigned long that can be expressed with the given number of bits.
*
* @param bitsPerValue the number of bits available for any given value.
* @return the maximum value for the given bits.
*/
public static long maxValue(int bitsPerValue) {
return bitsPerValue == 64 ? Long.MAX_VALUE : ~(~0L << bitsPerValue);
}
/**
* Copy src[srcPos:srcPos+len] into dest[destPos:destPos+len] using at
* most mem bytes.
*/
public static void copy(Reader src, int srcPos, Mutable dest, int destPos, int len, int mem) {
assert srcPos + len <= src.size();
assert destPos + len <= dest.size();
final int capacity = mem >>> 3;
if (capacity == 0) {
for (int i = 0; i < len; ++i) {
dest.set(destPos++, src.get(srcPos++));
}
} else if (len > 0) {
// use bulk operations
final long[] buf = new long[Math.min(capacity, len)];
copy(src, srcPos, dest, destPos, len, buf);
}
}
/**
* Same as {@link #copy(Reader, int, Mutable, int, int, int)} but using a pre-allocated buffer.
*/
static void copy(Reader src, int srcPos, Mutable dest, int destPos, int len, long[] buf) {
assert buf.length > 0;
int remaining = 0;
while (len > 0) {
final int read = src.get(srcPos, buf, remaining, Math.min(len, buf.length - remaining));
assert read > 0;
srcPos += read;
len -= read;
remaining += read;
final int written = dest.set(destPos, buf, 0, remaining);
assert written > 0;
destPos += written;
if (written < remaining) {
System.arraycopy(buf, written, buf, 0, remaining - written);
}
remaining -= written;
}
while (remaining > 0) {
final int written = dest.set(destPos, buf, 0, remaining);
destPos += written;
remaining -= written;
System.arraycopy(buf, written, buf, 0, remaining);
}
}
/**
* Check that the block size is a power of 2, in the right bounds, and return its log in base 2.
*/
static int checkBlockSize(int blockSize, int minBlockSize, int maxBlockSize) {
if (blockSize < minBlockSize || blockSize > maxBlockSize) {
throw new IllegalArgumentException("blockSize must be >= " + minBlockSize + " and <= " + maxBlockSize + ", got " + blockSize);
}
if ((blockSize & (blockSize - 1)) != 0) {
throw new IllegalArgumentException("blockSize must be a power of two, got " + blockSize);
}
return Integer.numberOfTrailingZeros(blockSize);
}
/**
* Return the number of blocks required to store size values on blockSize
* .
*/
static int numBlocks(long size, int blockSize) {
final int numBlocks = (int) (size / blockSize) + (size % blockSize == 0 ? 0 : 1);
if ((long) numBlocks * blockSize < size) {
throw new IllegalArgumentException("size is too large for this block size");
}
return numBlocks;
}
}