AbstractEncodedMessages.java
/* Copyright 2002-2022 CS GROUP
* Licensed to CS GROUP (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* CS 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.orekit.gnss.metric.parser;
import org.hipparchus.util.FastMath;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitMessages;
/** Encoded messages as a sequence of bytes.
* @author Luc Maisonobe
* @since 11.0
*/
public abstract class AbstractEncodedMessages implements EncodedMessage {
/** Current byte (as an int). */
private int current;
/** Remaining bits in current byte. */
private int remaining;
/** {@inheritDoc} */
@Override
public void start() {
this.remaining = 0;
}
/** Fetch the next byte from the message.
* @return next byte from the message, as a primitive integer,
* or -1 if end of data has been reached
*/
protected abstract int fetchByte();
/** {@inheritDoc} */
@Override
public long extractBits(final int n) {
// safety check
if (n > 63) {
throw new OrekitException(OrekitMessages.TOO_LARGE_DATA_TYPE, n);
}
// initialization
long value = 0l;
// bits gathering loop
int needed = n;
while (needed > 0) {
if (remaining == 0) {
// we need to fetch one more byte
final int read = fetchByte();
if (read == -1) {
// end was unexpected
throw new OrekitException(OrekitMessages.END_OF_ENCODED_MESSAGE);
}
current = read & 0xFF;
remaining = 8;
}
final int nbBits = FastMath.min(remaining, needed);
value = (value << nbBits) | (current >>> (8 - nbBits));
current = (current << nbBits) & 0xFF;
remaining -= nbBits;
needed -= nbBits;
}
return value;
}
}