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/* 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.
*
* <p>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.
*
* <p>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;
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 data, int[] sizeBits) {
if (!data.isDirect() || !data.isReadOnly()) {
throw new BrotliRuntimeException("data must be a direct read-only byte buffer");
}
// TODO: is that so?
if (sizeBits.length > MAX_DICTIONARY_WORD_LENGTH) {
throw new BrotliRuntimeException(
"sizeBits length must be at most " + MAX_DICTIONARY_WORD_LENGTH);
}
for (int i = 0; i < MIN_DICTIONARY_WORD_LENGTH; ++i) {
if (sizeBits[i] != 0) {
throw new BrotliRuntimeException("first " + MIN_DICTIONARY_WORD_LENGTH + " must be 0");
}
}
int[] dictionaryOffsets = Dictionary.offsets;
int[] dictionarySizeBits = Dictionary.sizeBits;
System.arraycopy(sizeBits, 0, dictionarySizeBits, 0, sizeBits.length);
int pos = 0;
int limit = data.capacity();
for (int i = 0; i < sizeBits.length; ++i) {
dictionaryOffsets[i] = pos;
int bits = dictionarySizeBits[i];
if (bits != 0) {
if (bits >= 31) {
throw new BrotliRuntimeException("sizeBits values must be less than 31");
}
pos += i << bits;
if (pos <= 0 || pos > limit) {
throw new BrotliRuntimeException("sizeBits is inconsistent: overflow");
}
}
}
for (int i = sizeBits.length; i < 32; ++i) {
dictionaryOffsets[i] = pos;
}
if (pos != limit) {
throw new BrotliRuntimeException("sizeBits is inconsistent: underflow");
}
Dictionary.data = data;
}
public static ByteBuffer getData() {
if (data != null) {
return data;
}
if (!DataLoader.OK) {
throw new BrotliRuntimeException("brotli dictionary is not set");
}
/* Might have been set when {@link DictionaryData} was loaded.*/
return data;
}
}
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