org.eclipse.jetty.http.compression.NBitIntegerEncoder Maven / Gradle / Ivy
//
// ========================================================================
// Copyright (c) 1995 Mort Bay Consulting Pty Ltd and others.
//
// This program and the accompanying materials are made available under the
// terms of the Eclipse Public License v. 2.0 which is available at
// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
// which is available at https://www.apache.org/licenses/LICENSE-2.0.
//
// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
// ========================================================================
//
package org.eclipse.jetty.http.compression;
import java.nio.ByteBuffer;
/**
* Used to encode integers as described in RFC7541.
*/
public class NBitIntegerEncoder
{
private NBitIntegerEncoder()
{
}
/**
* @param prefix the prefix used to encode this long.
* @param value the integer to encode.
* @return the number of octets it would take to encode the long.
*/
public static int octetsNeeded(int prefix, long value)
{
if (prefix <= 0 || prefix > 8)
throw new IllegalArgumentException();
int nbits = 0xFF >>> (8 - prefix);
value = value - nbits;
if (value < 0)
return 1;
if (value == 0)
return 2;
int lz = Long.numberOfLeadingZeros(value);
int log = 64 - lz;
// The return value is 1 for the prefix + the number of 7-bit groups necessary to encode the value.
return 1 + (log + 6) / 7;
}
/**
*
* @param buffer the buffer to encode into.
* @param prefix the prefix used to encode this long.
* @param value the long to encode into the buffer.
*/
public static void encode(ByteBuffer buffer, int prefix, long value)
{
if (prefix <= 0 || prefix > 8)
throw new IllegalArgumentException();
// If prefix is 8 we add an empty byte as we initially modify last byte from the buffer.
if (prefix == 8)
buffer.put((byte)0x00);
int bits = 0xFF >>> (8 - prefix);
int p = buffer.position() - 1;
if (value < bits)
{
buffer.put(p, (byte)((buffer.get(p) & ~bits) | value));
}
else
{
buffer.put(p, (byte)(buffer.get(p) | bits));
long length = value - bits;
while (true)
{
// The value of ~0x7F is different to 0x80 because of all the 1s from the MSB.
if ((length & ~0x7FL) == 0)
{
buffer.put((byte)length);
return;
}
else
{
buffer.put((byte)((length & 0x7F) | 0x80));
length >>>= 7;
}
}
}
}
}