| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF 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.apache.commons.compress.utils; |
| |
| import java.io.Closeable; |
| import java.io.IOException; |
| import java.io.InputStream; |
| import java.nio.ByteOrder; |
| |
| /** |
| * Reads bits from an InputStream. |
| * @since 1.10 |
| * @NotThreadSafe |
| */ |
| public class BitInputStream implements Closeable { |
| private static final int MAXIMUM_CACHE_SIZE = 63; // bits in long minus sign bit |
| private static final long[] MASKS = new long[MAXIMUM_CACHE_SIZE + 1]; |
| |
| static { |
| for (int i = 1; i <= MAXIMUM_CACHE_SIZE; i++) { |
| MASKS[i] = (MASKS[i - 1] << 1) + 1; |
| } |
| } |
| |
| private final InputStream in; |
| private final ByteOrder byteOrder; |
| private long bitsCached = 0; |
| private int bitsCachedSize = 0; |
| |
| /** |
| * Constructor taking an InputStream and its bit arrangement. |
| * @param in the InputStream |
| * @param byteOrder the bit arrangement across byte boundaries, |
| * either BIG_ENDIAN (aaaaabbb bb000000) or LITTLE_ENDIAN (bbbaaaaa 000000bb) |
| */ |
| public BitInputStream(final InputStream in, final ByteOrder byteOrder) { |
| this.in = in; |
| this.byteOrder = byteOrder; |
| } |
| |
| @Override |
| public void close() throws IOException { |
| in.close(); |
| } |
| |
| /** |
| * Clears the cache of bits that have been read from the |
| * underlying stream but not yet provided via {@link #readBits}. |
| */ |
| public void clearBitCache() { |
| bitsCached = 0; |
| bitsCachedSize = 0; |
| } |
| |
| /** |
| * Returns at most 63 bits read from the underlying stream. |
| * |
| * @param count the number of bits to read, must be a positive |
| * number not bigger than 63. |
| * @return the bits concatenated as a long using the stream's byte order. |
| * -1 if the end of the underlying stream has been reached before reading |
| * the requested number of bits |
| * @throws IOException on error |
| */ |
| public long readBits(final int count) throws IOException { |
| if (count < 0 || count > MAXIMUM_CACHE_SIZE) { |
| throw new IllegalArgumentException("count must not be negative or greater than " + MAXIMUM_CACHE_SIZE); |
| } |
| while (bitsCachedSize < count && bitsCachedSize < 57) { |
| final long nextByte = in.read(); |
| if (nextByte < 0) { |
| return nextByte; |
| } |
| if (byteOrder == ByteOrder.LITTLE_ENDIAN) { |
| bitsCached |= (nextByte << bitsCachedSize); |
| } else { |
| bitsCached <<= 8; |
| bitsCached |= nextByte; |
| } |
| bitsCachedSize += 8; |
| } |
| int overflowBits = 0; |
| long overflow = 0l; |
| if (bitsCachedSize < count) { |
| // bitsCachedSize >= 57 and left-shifting it 8 bits would cause an overflow |
| int bitsToAddCount = count - bitsCachedSize; |
| overflowBits = 8 - bitsToAddCount; |
| final long nextByte = in.read(); |
| if (nextByte < 0) { |
| return nextByte; |
| } |
| if (byteOrder == ByteOrder.LITTLE_ENDIAN) { |
| long bitsToAdd = nextByte & MASKS[bitsToAddCount]; |
| bitsCached |= (bitsToAdd << bitsCachedSize); |
| overflow = (nextByte >>> bitsToAddCount) & MASKS[overflowBits]; |
| } else { |
| bitsCached <<= bitsToAddCount; |
| long bitsToAdd = (nextByte >>> (overflowBits)) & MASKS[bitsToAddCount]; |
| bitsCached |= bitsToAdd; |
| overflow = nextByte & MASKS[overflowBits]; |
| } |
| bitsCachedSize = count; |
| } |
| |
| final long bitsOut; |
| if (overflowBits == 0) { |
| if (byteOrder == ByteOrder.LITTLE_ENDIAN) { |
| bitsOut = (bitsCached & MASKS[count]); |
| bitsCached >>>= count; |
| } else { |
| bitsOut = (bitsCached >> (bitsCachedSize - count)) & MASKS[count]; |
| } |
| bitsCachedSize -= count; |
| } else { |
| bitsOut = bitsCached & MASKS[count]; |
| bitsCached = overflow; |
| bitsCachedSize = overflowBits; |
| } |
| return bitsOut; |
| } |
| } |