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327 lines
12 KiB
C#
327 lines
12 KiB
C#
/* This file is part of libmspack.
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* (C) 2003-2013 Stuart Caie.
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*
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* The LZX method was created by Jonathan Forbes and Tomi Poutanen, adapted
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* by Microsoft Corporation.
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*
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* libmspack is free software { get; set; } you can redistribute it and/or modify it under
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* the terms of the GNU Lesser General Public License (LGPL) version 2.1
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*
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* For further details, see the file COPYING.LIB distributed with libmspack
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*/
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using System;
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namespace LibMSPackSharp.Compression
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{
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public abstract class CompressionStream : BaseDecompressState
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{
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private const int CHAR_BIT = 8;
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public const int BITBUF_WIDTH = 4 * CHAR_BIT;
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#region I/O buffering
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public byte[] InputBuffer { get; set; }
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public uint InputBufferSize { get; set; }
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public int InputPointer { get; set; }
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public int InputLength { get; set; }
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public int OutputPointer { get; set; }
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public int OutputLength { get; set; }
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public uint BitBuffer { get; set; }
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public int BitsLeft { get; set; }
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/// <summary>
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/// Have we reached the end of input?
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/// </summary>
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public int InputEnd { get; set; }
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#endregion
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// TODO: These should be in a separate file
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#region ReadBits Methods
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/* This header defines macros that read data streams by
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* the individual bits
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*
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* INIT_BITS initialises bitstream state in state structure
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* STORE_BITS stores bitstream state in state structure
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* RESTORE_BITS restores bitstream state from state structure
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* ENSURE_BITS(n) ensure there are at least N bits in the bit buffer
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* READ_BITS(var,n) takes N bits from the buffer and puts them in var
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* PEEK_BITS(n) extracts without removing N bits from the bit buffer
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* REMOVE_BITS(n) removes N bits from the bit buffer
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*
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* READ_BITS simply calls ENSURE_BITS, PEEK_BITS and REMOVE_BITS,
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* which means it's limited to reading the number of bits you can
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* ensure at any one time. It also fails if asked to read zero bits.
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* If you need to read zero bits, or more bits than can be ensured in
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* one go, use READ_MANY_BITS instead.
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*
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* These macros have variable names baked into them, so to use them
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* you have to define some macros:
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* - BITS_TYPE: the type name of your state structure
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* - BITS_VAR: the variable that points to your state structure
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* - define BITS_ORDER_MSB if bits are read from the MSB, or
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* define BITS_ORDER_LSB if bits are read from the LSB
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* - READ_BYTES: some code that reads more data into the bit buffer,
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* it should use READ_IF_NEEDED (calls read_input if the byte buffer
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* is empty), then INJECT_BITS(data,n) to put data from the byte
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* buffer into the bit buffer.
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*
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* You also need to define some variables and structure members:
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* - byte[] i_ptr; // current position in the byte buffer
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* - byte[] i_end; // end of the byte buffer
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* - uint bit_buffer; // the bit buffer itself
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* - uint bits_left; // number of bits remaining
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*
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* If you use read_input() and READ_IF_NEEDED, they also expect these
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* structure members:
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* - struct mspack_system *sys; // to access sys->read()
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* - uint error; // to record/return read errors
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* - byte input_end; // to mark reaching the EOF
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* - byte[] inbuf; // the input byte buffer
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* - uint inbuf_size; // the size of the input byte buffer
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*
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* Your READ_BYTES implementation should read data from *i_ptr and
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* put them in the bit buffer. READ_IF_NEEDED will call read_input()
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* if i_ptr reaches i_end, and will fill up inbuf and set i_ptr to
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* the start of inbuf and i_end to the end of inbuf.
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*
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* If you're reading in MSB order, the routines work by using the area
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* beyond the MSB and the LSB of the bit buffer as a free source of
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* zeroes when shifting. This avoids having to mask any bits. So we
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* have to know the bit width of the bit buffer variable. We use
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* <limits.h> and CHAR_BIT to find the size of the bit buffer in bits.
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*
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* If you are reading in LSB order, bits need to be masked. Normally
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* this is done by computing the mask: N bits are masked by the value
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* (1<<N)-1). However, you can define BITS_LSB_TABLE to use a lookup
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* table instead of computing this. This adds two new macros,
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* PEEK_BITS_T and READ_BITS_T which work the same way as PEEK_BITS
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* and READ_BITS, except they use this lookup table. This is useful if
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* you need to look up a number of bits that are only known at
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* runtime, so the bit mask can't be turned into a constant by the
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* compiler.
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* The bit buffer datatype should be at least 32 bits wide: it must be
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* possible to ENSURE_BITS(17), so it must be possible to add 16 new bits
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* to the bit buffer when the bit buffer already has 1 to 15 bits left.
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*/
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public Error ReadInput()
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{
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int read = System.Read(InputFileHandle, InputBuffer, 0, (int)InputBufferSize);
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if (read < 0)
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return Error = Error.MSPACK_ERR_READ;
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// We might overrun the input stream by asking for bits we don't use,
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// so fake 2 more bytes at the end of input
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if (read == 0)
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{
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if (InputEnd != 0)
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{
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Console.WriteLine("Out of input bytes");
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return Error = Error.MSPACK_ERR_READ;
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}
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else
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{
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read = 2;
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InputBuffer[0] = InputBuffer[1] = 0;
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InputEnd = 1;
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}
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}
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// Update i_ptr and i_end
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InputPointer = 0;
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InputLength = read;
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return Error = Error.MSPACK_ERR_OK;
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}
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#endregion
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// TODO: These should be in a separate file
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#region ReadHuff Methods
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public const int HUFF_MAXBITS = 16;
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/// <summary>
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/// This function was originally coded by David Tritscher.
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///
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/// It builds a fast huffman decoding table from
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/// a canonical huffman code lengths table.
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/// </summary>
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/// <param name="nsyms">total number of symbols in this huffman tree.</param>
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/// <param name="nbits">any symbols with a code length of nbits or less can be decoded in one lookup of the table.</param>
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/// <param name="length">A table to get code lengths from [0 to nsyms-1]</param>
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/// <param name="table">
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/// The table to fill up with decoded symbols and pointers.
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/// Should be ((1<<nbits) + (nsyms*2)) in length.
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/// </param>
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/// <returns>true for OK or false for error</returns>
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public static bool MakeDecodeTable(int nsyms, int nbits, byte[] length, ushort[] table, bool msb)
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{
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ushort sym, next_symbol;
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uint leaf, fill;
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uint reverse; // Only used when !msb
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byte bit_num;
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uint pos = 0; // The current position in the decode table
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uint table_mask = (uint)1 << nbits;
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uint bit_mask = table_mask >> 1; // Don't do 0 length codes
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// Fill entries for codes short enough for a direct mapping
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for (bit_num = 1; bit_num <= nbits; bit_num++)
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{
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for (sym = 0; sym < nsyms; sym++)
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{
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if (length[sym] != bit_num)
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continue;
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if (msb)
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{
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leaf = pos;
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}
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else
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{
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// Reverse the significant bits
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fill = length[sym];
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reverse = pos >> (nbits - (byte)fill);
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leaf = 0;
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do
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{
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leaf <<= 1;
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leaf |= reverse & 1;
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reverse >>= 1;
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} while (--fill != 0);
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}
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if ((pos += bit_mask) > table_mask)
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return false; // Table overrun
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// Fill all possible lookups of this symbol with the symbol itself
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if (msb)
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{
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for (fill = bit_mask; fill-- > 0;)
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{
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table[leaf++] = sym;
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}
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}
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else
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{
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fill = bit_mask;
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next_symbol = (ushort)(1 << bit_num);
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do
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{
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table[leaf] = sym;
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leaf += next_symbol;
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} while (--fill != 0);
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}
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}
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bit_mask >>= 1;
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}
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// Exit with success if table is now complete
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if (pos == table_mask)
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return true;
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// Mark all remaining table entries as unused
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for (sym = (ushort)pos; sym < table_mask; sym++)
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{
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if (msb)
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{
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table[sym] = 0xFFFF;
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}
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else
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{
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reverse = sym;
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leaf = 0;
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fill = (uint)nbits;
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do
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{
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leaf <<= 1;
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leaf |= reverse & 1;
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reverse >>= 1;
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} while (--fill != 0);
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table[leaf] = 0xFFFF;
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}
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}
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// next_symbol = base of allocation for long codes
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next_symbol = ((table_mask >> 1) < nsyms) ? (ushort)nsyms : (ushort)(table_mask >> 1);
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// Give ourselves room for codes to grow by up to 16 more bits.
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// codes now start at bit nbits+16 and end at (nbits+16-codelength)
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pos <<= 16;
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table_mask <<= 16;
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bit_mask = 1 << 15;
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for (bit_num = (byte)(nbits + 1); bit_num <= HUFF_MAXBITS; bit_num++)
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{
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for (sym = 0; sym < nsyms; sym++)
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{
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if (length[sym] != bit_num)
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continue;
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if (pos >= table_mask)
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return false; // Table overflow
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if (msb)
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{
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leaf = pos >> 16;
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}
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else
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{
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// leaf = the first nbits of the code, reversed
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reverse = pos >> 16;
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leaf = 0;
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fill = (uint)nbits;
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do
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{
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leaf <<= 1;
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leaf |= reverse & 1;
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reverse >>= 1;
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} while (--fill != 0);
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}
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for (fill = 0; fill < (bit_num - nbits); fill++)
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{
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// If this path hasn't been taken yet, 'allocate' two entries
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if (table[leaf] == 0xFFFF)
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{
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table[(next_symbol << 1)] = 0xFFFF;
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table[(next_symbol << 1) + 1] = 0xFFFF;
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table[leaf] = (ushort)next_symbol++;
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}
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// Follow the path and select either left or right for next bit
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leaf = (uint)(table[leaf] << 1);
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if (((pos >> (15 - (int)fill)) & 1) != 0)
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leaf++;
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}
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table[leaf] = sym;
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pos += bit_mask;
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}
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bit_mask >>= 1;
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}
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// Full table?
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return pos == table_mask;
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}
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#endregion
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}
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}
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