// StreamManipulator.cs
// Copyright (C) 2001 Mike Krueger
//
// This file was translated from java, it was part of the GNU Classpath
// Copyright (C) 2001 Free Software Foundation, Inc.
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library. Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
//
// As a special exception, the copyright holders of this library give you
// permission to link this library with independent modules to produce an
// executable, regardless of the license terms of these independent
// modules, and to copy and distribute the resulting executable under
// terms of your choice, provided that you also meet, for each linked
// independent module, the terms and conditions of the license of that
// module. An independent module is a module which is not derived from
// or based on this library. If you modify this library, you may extend
// this exception to your version of the library, but you are not
// obligated to do so. If you do not wish to do so, delete this
// exception statement from your version.
using System;
namespace ICSharpCode.SharpZipLib.Zip.Compression.Streams
{
/// <summary>
/// This class allows us to retrieve a specified amount of bits from
/// the input buffer, as well as copy big byte blocks.
///
/// It uses an int buffer to store up to 31 bits for direct
/// manipulation. This guarantees that we can get at least 16 bits,
/// but we only need at most 15, so this is all safe.
///
/// There are some optimizations in this class, for example, you must
/// never peek more then 8 bits more than needed, and you must first
/// peek bits before you may drop them. This is not a general purpose
/// class but optimized for the behaviour of the Inflater.
///
/// authors of the original java version : John Leuner, Jochen Hoenicke
/// </summary>
public class StreamManipulator
{
private byte[] window;
private int window_start = 0;
private int window_end = 0;
private uint buffer = 0;
private int bits_in_buffer = 0;
/// <summary>
/// Get the next n bits but don't increase input pointer. n must be
/// less or equal 16 and if you if this call succeeds, you must drop
/// at least n-8 bits in the next call.
/// </summary>
/// <returns>
/// the value of the bits, or -1 if not enough bits available. */
/// </returns>
public int PeekBits(int n)
{
if (bits_in_buffer < n) {
if (window_start == window_end) {
return -1; // ok
}
buffer |= (uint)((window[window_start++] & 0xff |
(window[window_start++] & 0xff) << 8) << bits_in_buffer);
bits_in_buffer += 16;
}
return (int)(buffer & ((1 << n) - 1));
}
/// <summary>
/// Drops the next n bits from the input. You should have called peekBits
/// with a bigger or equal n before, to make sure that enough bits are in
/// the bit buffer.
/// </summary>
public void DropBits(int n)
{
buffer >>= n;
bits_in_buffer -= n;
}
/// <summary>
/// Gets the next n bits and increases input pointer. This is equivalent
/// to peekBits followed by dropBits, except for correct error handling.
/// </summary>
/// <returns>
/// the value of the bits, or -1 if not enough bits available.
/// </returns>
public int GetBits(int n)
{
int bits = PeekBits(n);
if (bits >= 0) {
DropBits(n);
}
return bits;
}
/// <summary>
/// Gets the number of bits available in the bit buffer. This must be
/// only called when a previous peekBits() returned -1.
/// </summary>
/// <returns>
/// the number of bits available.
/// </returns>
public int AvailableBits {
get {
return bits_in_buffer;
}
}
/// <summary>
/// Gets the number of bytes available.
/// </summary>
/// <returns>
/// the number of bytes available.
/// </returns>
public int AvailableBytes {
get {
return window_end - window_start + (bits_in_buffer >> 3);
}
}
/// <summary>
/// Skips to the next byte boundary.
/// </summary>
public void SkipToByteBoundary()
{
buffer >>= (bits_in_buffer & 7);
bits_in_buffer &= ~7;
}
public bool IsNeedingInput {
get {
return window_start == window_end;
}
}
/// <summary>
/// Copies length bytes from input buffer to output buffer starting
/// at output[offset]. You have to make sure, that the buffer is
/// byte aligned. If not enough bytes are available, copies fewer
/// bytes.
/// </summary>
/// <param name="output">
/// the buffer.
/// </param>
/// <param name="offset">
/// the offset in the buffer.
/// </param>
/// <param name="length">
/// the length to copy, 0 is allowed.
/// </param>
/// <returns>
/// the number of bytes copied, 0 if no byte is available.
/// </returns>
public int CopyBytes(byte[] output, int offset, int length)
{
if (length < 0) {
throw new ArgumentOutOfRangeException("length negative");
}
if ((bits_in_buffer & 7) != 0) {
/* bits_in_buffer may only be 0 or 8 */
throw new InvalidOperationException("Bit buffer is not aligned!");
}
int count = 0;
while (bits_in_buffer > 0 && length > 0) {
output[offset++] = (byte) buffer;
buffer >>= 8;
bits_in_buffer -= 8;
length--;
count++;
}
if (length == 0) {
return count;
}
int avail = window_end - window_start;
if (length > avail) {
length = avail;
}
System.Array.Copy(window, window_start, output, offset, length);
window_start += length;
if (((window_start - window_end) & 1) != 0) {
/* We always want an even number of bytes in input, see peekBits */
buffer = (uint)(window[window_start++] & 0xff);
bits_in_buffer = 8;
}
return count + length;
}
public StreamManipulator()
{
}
public void Reset()
{
buffer = (uint)(window_start = window_end = bits_in_buffer = 0);
}
public void SetInput(byte[] buf, int off, int len)
{
if (window_start < window_end) {
throw new InvalidOperationException("Old input was not completely processed");
}
int end = off + len;
/* We want to throw an ArrayIndexOutOfBoundsException early. The
* check is very tricky: it also handles integer wrap around.
*/
if (0 > off || off > end || end > buf.Length) {
throw new ArgumentOutOfRangeException();
}
if ((len & 1) != 0) {
/* We always want an even number of bytes in input, see peekBits */
buffer |= (uint)((buf[off++] & 0xff) << bits_in_buffer);
bits_in_buffer += 8;
}
window = buf;
window_start = off;
window_end = end;
}
}
}