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Tom Tromey
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libjava/classpath/java/util/zip/StreamManipulator.java
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libjava/classpath/java/util/zip/StreamManipulator.java
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/* java.util.zip.StreamManipulator
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Copyright (C) 2001 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package java.util.zip;
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/**
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* This class allows us to retrieve a specified amount of bits from
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* the input buffer, as well as copy big byte blocks.
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*
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* It uses an int buffer to store up to 31 bits for direct
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* manipulation. This guarantees that we can get at least 16 bits,
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* but we only need at most 15, so this is all safe.
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*
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* There are some optimizations in this class, for example, you must
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* never peek more then 8 bits more than needed, and you must first
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* peek bits before you may drop them. This is not a general purpose
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* class but optimized for the behaviour of the Inflater.
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*
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* @author John Leuner, Jochen Hoenicke
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*/
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class StreamManipulator
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{
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private byte[] window;
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private int window_start = 0;
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private int window_end = 0;
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private int buffer = 0;
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private int bits_in_buffer = 0;
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/**
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* Get the next n bits but don't increase input pointer. n must be
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* less or equal 16 and if you if this call succeeds, you must drop
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* at least n-8 bits in the next call.
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*
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* @return the value of the bits, or -1 if not enough bits available. */
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public final int peekBits(int n)
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{
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if (bits_in_buffer < n)
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{
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if (window_start == window_end)
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return -1;
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buffer |= (window[window_start++] & 0xff
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| (window[window_start++] & 0xff) << 8) << bits_in_buffer;
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bits_in_buffer += 16;
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}
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return buffer & ((1 << n) - 1);
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}
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/* Drops the next n bits from the input. You should have called peekBits
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* with a bigger or equal n before, to make sure that enough bits are in
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* the bit buffer.
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*/
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public final void dropBits(int n)
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{
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buffer >>>= n;
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bits_in_buffer -= n;
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}
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/**
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* Gets the next n bits and increases input pointer. This is equivalent
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* to peekBits followed by dropBits, except for correct error handling.
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* @return the value of the bits, or -1 if not enough bits available.
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*/
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public final int getBits(int n)
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{
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int bits = peekBits(n);
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if (bits >= 0)
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dropBits(n);
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return bits;
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}
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/**
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* Gets the number of bits available in the bit buffer. This must be
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* only called when a previous peekBits() returned -1.
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* @return the number of bits available.
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*/
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public final int getAvailableBits()
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{
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return bits_in_buffer;
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}
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/**
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* Gets the number of bytes available.
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* @return the number of bytes available.
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*/
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public final int getAvailableBytes()
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{
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return window_end - window_start + (bits_in_buffer >> 3);
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}
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/**
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* Skips to the next byte boundary.
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*/
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public void skipToByteBoundary()
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{
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buffer >>= (bits_in_buffer & 7);
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bits_in_buffer &= ~7;
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}
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public final boolean needsInput() {
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return window_start == window_end;
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}
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/* Copies length bytes from input buffer to output buffer starting
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* at output[offset]. You have to make sure, that the buffer is
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* byte aligned. If not enough bytes are available, copies fewer
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* bytes.
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* @param length the length to copy, 0 is allowed.
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* @return the number of bytes copied, 0 if no byte is available.
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*/
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public int copyBytes(byte[] output, int offset, int length)
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{
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if (length < 0)
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throw new IllegalArgumentException("length negative");
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if ((bits_in_buffer & 7) != 0)
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/* bits_in_buffer may only be 0 or 8 */
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throw new IllegalStateException("Bit buffer is not aligned!");
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int count = 0;
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while (bits_in_buffer > 0 && length > 0)
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{
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output[offset++] = (byte) buffer;
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buffer >>>= 8;
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bits_in_buffer -= 8;
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length--;
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count++;
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}
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if (length == 0)
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return count;
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int avail = window_end - window_start;
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if (length > avail)
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length = avail;
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System.arraycopy(window, window_start, output, offset, length);
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window_start += length;
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if (((window_start - window_end) & 1) != 0)
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{
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/* We always want an even number of bytes in input, see peekBits */
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buffer = (window[window_start++] & 0xff);
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bits_in_buffer = 8;
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}
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return count + length;
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}
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public StreamManipulator()
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{
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}
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public void reset()
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{
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window_start = window_end = buffer = bits_in_buffer = 0;
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}
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public void setInput(byte[] buf, int off, int len)
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{
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if (window_start < window_end)
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throw new IllegalStateException
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("Old input was not completely processed");
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int end = off + len;
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/* We want to throw an ArrayIndexOutOfBoundsException early. The
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* check is very tricky: it also handles integer wrap around.
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*/
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if (0 > off || off > end || end > buf.length)
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throw new ArrayIndexOutOfBoundsException();
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if ((len & 1) != 0)
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{
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/* We always want an even number of bytes in input, see peekBits */
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buffer |= (buf[off++] & 0xff) << bits_in_buffer;
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bits_in_buffer += 8;
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}
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window = buf;
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window_start = off;
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window_end = end;
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}
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}
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