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245 lines
7.5 KiB
C#
245 lines
7.5 KiB
C#
// StreamManipulator.cs
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// Copyright (C) 2001 Mike Krueger
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//
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// This file was translated from java, it was part of the GNU Classpath
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// Copyright (C) 2001 Free Software Foundation, Inc.
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//
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// This program is free software; you can redistribute it and/or
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// modify it under the terms of the GNU General Public License
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// as published by the Free Software Foundation; either version 2
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// of the License, or (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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//
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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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//
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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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using System;
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namespace ICSharpCode.SharpZipLib.Zip.Compression.Streams
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{
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/// <summary>
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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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/// authors of the original java version : John Leuner, Jochen Hoenicke
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/// </summary>
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public 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 uint buffer = 0;
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private int bits_in_buffer = 0;
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/// <summary>
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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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/// </summary>
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/// <returns>
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/// the value of the bits, or -1 if not enough bits available. */
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/// </returns>
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public int PeekBits(int n)
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{
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if (bits_in_buffer < n) {
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if (window_start == window_end) {
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return -1; // ok
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}
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buffer |= (uint)((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 (int)(buffer & ((1 << n) - 1));
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}
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/// <summary>
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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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/// </summary>
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public 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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/// <summary>
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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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/// </summary>
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/// <returns>
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/// the value of the bits, or -1 if not enough bits available.
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/// </returns>
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public 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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}
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return bits;
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}
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/// <summary>
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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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/// </summary>
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/// <returns>
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/// the number of bits available.
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/// </returns>
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public int AvailableBits {
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get {
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return bits_in_buffer;
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}
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}
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/// <summary>
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/// Gets the number of bytes available.
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/// </summary>
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/// <returns>
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/// the number of bytes available.
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/// </returns>
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public int AvailableBytes {
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get {
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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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/// <summary>
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/// Skips to the next byte boundary.
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/// </summary>
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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 bool IsNeedingInput {
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get {
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return window_start == window_end;
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}
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}
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/// <summary>
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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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/// </summary>
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/// <param name="output">
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/// the buffer.
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/// </param>
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/// <param name="offset">
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/// the offset in the buffer.
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/// </param>
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/// <param name="length">
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/// the length to copy, 0 is allowed.
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/// </param>
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/// <returns>
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/// the number of bytes copied, 0 if no byte is available.
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/// </returns>
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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 ArgumentOutOfRangeException("length negative");
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}
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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 InvalidOperationException("Bit buffer is not aligned!");
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}
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int count = 0;
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while (bits_in_buffer > 0 && length > 0) {
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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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}
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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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}
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System.Array.Copy(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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/* We always want an even number of bytes in input, see peekBits */
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buffer = (uint)(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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buffer = (uint)(window_start = window_end = 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 InvalidOperationException("Old input was not completely processed");
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}
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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 ArgumentOutOfRangeException();
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}
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if ((len & 1) != 0) {
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/* We always want an even number of bytes in input, see peekBits */
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buffer |= (uint)((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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}
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