root/trunk/Updater/ICSharpCode.SharpZipLib/Zip/Compression/Streams/StreamManipulator.cs @ 597

// 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 number 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 than 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
        {
                #region Constructors
                /// <summary>
                /// Constructs a default StreamManipulator with all buffers empty
                /// </summary>
                public StreamManipulator()
                {
                }
                #endregion

                /// <summary>
                /// Get the next sequence of bits but don't increase input pointer.  bitCount must be
                /// less or equal 16 and if this call succeeds, you must drop
                /// at least n - 8 bits in the next call.
                /// </summary>
                /// <param name="bitCount">The number of bits to peek.</param>
                /// <returns>
                /// the value of the bits, or -1 if not enough bits available.  */
                /// </returns>
                public int PeekBits(int bitCount)
                {
                        if (bitsInBuffer_ < bitCount) {
                                if (windowStart_ == windowEnd_) {
                                        return -1; // ok
                                }
                                buffer_ |= (uint)((window_[windowStart_++] & 0xff |
                                                                 (window_[windowStart_++] & 0xff) << 8) << bitsInBuffer_);
                                bitsInBuffer_ += 16;
                        }
                        return (int)(buffer_ & ((1 << bitCount) - 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>
                /// <param name="bitCount">The number of bits to drop.</param>
                public void DropBits(int bitCount)
                {
                        buffer_ >>= bitCount;
                        bitsInBuffer_ -= bitCount;
                }
                
                /// <summary>
                /// Gets the next n bits and increases input pointer.  This is equivalent
                /// to <see cref="PeekBits"/> followed by <see cref="DropBits"/>, except for correct error handling.
                /// </summary>
                /// <param name="bitCount">The number of bits to retrieve.</param>
                /// <returns>
                /// the value of the bits, or -1 if not enough bits available.
                /// </returns>
                public int GetBits(int bitCount)
                {
                        int bits = PeekBits(bitCount);
                        if (bits >= 0) {
                                DropBits(bitCount);
                        }
                        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 bitsInBuffer_;
                        }
                }
                
                /// <summary>
                /// Gets the number of bytes available.
                /// </summary>
                /// <returns>
                /// The number of bytes available.
                /// </returns>
                public int AvailableBytes {
                        get {
                                return windowEnd_ - windowStart_ + (bitsInBuffer_ >> 3);
                        }
                }
                
                /// <summary>
                /// Skips to the next byte boundary.
                /// </summary>
                public void SkipToByteBoundary()
                {
                        buffer_ >>= (bitsInBuffer_ & 7);
                        bitsInBuffer_ &= ~7;
                }

                /// <summary>
                /// Returns true when SetInput can be called
                /// </summary>
                public bool IsNeedingInput {
                        get {
                                return windowStart_ == windowEnd_;
                        }
                }
                
                /// <summary>
                /// Copies 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 to copy bytes to.
                /// </param>
                /// <param name="offset">
                /// The offset in the buffer at which copying starts
                /// </param>
                /// <param name="length">
                /// The length to copy, 0 is allowed.
                /// </param>
                /// <returns>
                /// The number of bytes copied, 0 if no bytes were available.
                /// </returns>
                /// <exception cref="ArgumentOutOfRangeException">
                /// Length is less than zero
                /// </exception>
                /// <exception cref="InvalidOperationException">
                /// Bit buffer isnt byte aligned
                /// </exception>
                public int CopyBytes(byte[] output, int offset, int length)
                {
                        if (length < 0) {
                                throw new ArgumentOutOfRangeException("length");
                        }

                        if ((bitsInBuffer_ & 7) != 0) {
                                // bits_in_buffer may only be 0 or a multiple of 8
                                throw new InvalidOperationException("Bit buffer is not byte aligned!");
                        }
                        
                        int count = 0;
                        while ((bitsInBuffer_ > 0) && (length > 0)) {
                                output[offset++] = (byte) buffer_;
                                buffer_ >>= 8;
                                bitsInBuffer_ -= 8;
                                length--;
                                count++;
                        }
                        
                        if (length == 0) {
                                return count;
                        }
                        
                        int avail = windowEnd_ - windowStart_;
                        if (length > avail) {
                                length = avail;
                        }
                        System.Array.Copy(window_, windowStart_, output, offset, length);
                        windowStart_ += length;
                        
                        if (((windowStart_ - windowEnd_) & 1) != 0) {
                                // We always want an even number of bytes in input, see peekBits
                                buffer_ = (uint)(window_[windowStart_++] & 0xff);
                                bitsInBuffer_ = 8;
                        }
                        return count + length;
                }
                
                /// <summary>
                /// Resets state and empties internal buffers
                /// </summary>
                public void Reset()
                {
                        buffer_ = 0;
                        windowStart_ = windowEnd_ = bitsInBuffer_ = 0;
                }

                /// <summary>
                /// Add more input for consumption.
                /// Only call when IsNeedingInput returns true
                /// </summary>
                /// <param name="buffer">data to be input</param>
                /// <param name="offset">offset of first byte of input</param>
                /// <param name="count">number of bytes of input to add.</param>
                public void SetInput(byte[] buffer, int offset, int count)
                {
                        if ( buffer == null ) {
                                throw new ArgumentNullException("buffer");
                        }

                        if ( offset < 0 ) {
#if NETCF_1_0
                                throw new ArgumentOutOfRangeException("offset");
#else
                                throw new ArgumentOutOfRangeException("offset", "Cannot be negative");
#endif                          
                        }

                        if ( count < 0 ) {
#if NETCF_1_0
                                throw new ArgumentOutOfRangeException("count");
#else
                                throw new ArgumentOutOfRangeException("count", "Cannot be negative");
#endif                          
                        }

                        if (windowStart_ < windowEnd_) {
                                throw new InvalidOperationException("Old input was not completely processed");
                        }
                        
                        int end = offset + count;
                        
                        // We want to throw an ArrayIndexOutOfBoundsException early.
                        // Note the check also handles integer wrap around.
                        if ((offset > end) || (end > buffer.Length) ) {
                                throw new ArgumentOutOfRangeException("count");
                        }
                        
                        if ((count & 1) != 0) {
                                // We always want an even number of bytes in input, see PeekBits
                                buffer_ |= (uint)((buffer[offset++] & 0xff) << bitsInBuffer_);
                                bitsInBuffer_ += 8;
                        }
                        
                        window_ = buffer;
                        windowStart_ = offset;
                        windowEnd_ = end;
                }

                #region Instance Fields
                private byte[] window_;
                private int windowStart_;
                private int windowEnd_;

                private uint buffer_;
                private int bitsInBuffer_;
                #endregion
        }
}