org.brotli.dec.Dictionary Maven / Gradle / Ivy
/* Copyright 2015 Google Inc. All Rights Reserved.
Distributed under MIT license.
See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
*/
package org.brotli.dec;
import java.nio.ByteBuffer;
/**
* Collection of static dictionary words.
*
* Dictionary content is loaded from binary resource when {@link #getData()} is executed for the
* first time. Consequently, it saves memory and CPU in case dictionary is not required.
*
*
One possible drawback is that multiple threads that need dictionary data may be blocked (only
* once in each classworld). To avoid this, it is enough to call {@link #getData()} proactively.
*/
public final class Dictionary {
static final int MIN_DICTIONARY_WORD_LENGTH = 4;
static final int MAX_DICTIONARY_WORD_LENGTH = 31;
private static ByteBuffer data = ByteBuffer.allocateDirect(0);
static final int[] offsets = new int[32];
static final int[] sizeBits = new int[32];
private static class DataLoader {
static final boolean OK;
static {
boolean ok = true;
try {
Class.forName(Dictionary.class.getPackage().getName() + ".DictionaryData");
} catch (Throwable ex) {
ok = false;
}
OK = ok;
}
}
public static void setData(ByteBuffer newData, int[] newSizeBits) {
if ((Utils.isDirect(newData) == 0) || (Utils.isReadOnly(newData) == 0)) {
throw new BrotliRuntimeException("newData must be a direct read-only byte buffer");
}
// TODO: is that so?
if (newSizeBits.length > MAX_DICTIONARY_WORD_LENGTH) {
throw new BrotliRuntimeException(
"sizeBits length must be at most " + String.valueOf(MAX_DICTIONARY_WORD_LENGTH));
}
for (int i = 0; i < MIN_DICTIONARY_WORD_LENGTH; ++i) {
if (newSizeBits[i] != 0) {
throw new BrotliRuntimeException(
"first " + String.valueOf(MIN_DICTIONARY_WORD_LENGTH) + " must be 0");
}
}
final int[] dictionaryOffsets = Dictionary.offsets;
final int[] dictionarySizeBits = Dictionary.sizeBits;
System.arraycopy(newSizeBits, 0, dictionarySizeBits, 0, newSizeBits.length);
int pos = 0;
final int limit = newData.capacity();
for (int i = 0; i < newSizeBits.length; ++i) {
dictionaryOffsets[i] = pos;
final int bits = dictionarySizeBits[i];
if (bits != 0) {
if (bits >= 31) {
throw new BrotliRuntimeException("newSizeBits values must be less than 31");
}
pos += i << bits;
if (pos <= 0 || pos > limit) {
throw new BrotliRuntimeException("newSizeBits is inconsistent: overflow");
}
}
}
for (int i = newSizeBits.length; i < 32; ++i) {
dictionaryOffsets[i] = pos;
}
if (pos != limit) {
throw new BrotliRuntimeException("newSizeBits is inconsistent: underflow");
}
Dictionary.data = newData;
}
public static ByteBuffer getData() {
if (data.capacity() != 0) {
return data;
}
if (!DataLoader.OK) {
throw new BrotliRuntimeException("brotli dictionary is not set");
}
/* Might have been set when {@link DictionaryData} was loaded.*/
return data;
}
}