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/*
* Copyright (C) 2019 The Android Open Source Project
*
* Licensed 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.android.server.integrity.model;
import java.io.IOException;
import java.io.InputStream;
/** A wrapper class for reading a stream of bits.
*
* Note: this class reads from underlying stream byte-by-byte. It is advised to apply buffering
* to underlying streams.
*/
public class BitInputStream {
private long mBitsRead;
private InputStream mInputStream;
private byte mCurrentByte;
public BitInputStream(InputStream inputStream) {
mInputStream = inputStream;
}
/**
* Read the next number of bits from the stream.
*
* @param numOfBits The number of bits to read.
* @return The value read from the stream.
*/
public int getNext(int numOfBits) throws IOException {
int component = 0;
int count = 0;
while (count++ < numOfBits) {
if (mBitsRead % 8 == 0) {
mCurrentByte = getNextByte();
}
int offset = 7 - (int) (mBitsRead % 8);
component <<= 1;
component |= (mCurrentByte >>> offset) & 1;
mBitsRead++;
}
return component;
}
/** Check if there are bits left in the stream. */
public boolean hasNext() throws IOException {
return mInputStream.available() > 0;
}
private byte getNextByte() throws IOException {
return (byte) mInputStream.read();
}
}