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Add Util method for determining max compressed size (hyperxpro#95)
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hyperxpro authored Mar 3, 2023
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/*
* Copyright (c) 2020-2023, Aayush Atharva
*
* Brotli4j 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 com.aayushatharva.brotli4j.common;

/**
* Utilities class for Brotli4j
*/
public final class Utils {

/**
* Returns the maximum compressed size for the given input size.
* <p></p>
* This method is based on the original implementation of the Brotli library and works only
* for direct compression, not stream compression. This is useful to allocating buffers for compressed data.
*
* @param input_size The input size.
* @return The maximum compressed size.
* @throws IllegalArgumentException If the input size is negative.
*/
public static int maxCompressedSize(int input_size) {
if (input_size < 0) {
throw new IllegalArgumentException("Input size cannot be negative");
}

/* [window bits / empty metadata] + N * [uncompressed] + [last empty] */
int num_large_blocks = input_size >> 14;
int overhead = 2 + (4 * num_large_blocks) + 3 + 1;
int result = input_size + overhead;
if (input_size == 0) return 2;
return (result < input_size) ? 0 : result;
}

private Utils() {
// Prevent outside initialization
}
}

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