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BDK will allow developers to use the full collection of drivers, with limited editing, if any, for making payloads for Nintendo Switch. Using a single source for everything will also help decoupling Switch specific code and easily port it to other Tegra X1/X1+ platforms. And maybe even to lower targets. Everything is now centrilized into bdk folder. Every module or project can utilize it by simply including it. This is just the start and it will continue to improve.
180 lines
6.5 KiB
C
180 lines
6.5 KiB
C
/*************************************************************************
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* Name: lz.c
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* Author: Marcus Geelnard
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* Description: LZ77 coder/decoder implementation.
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* Reentrant: Yes
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*
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* The LZ77 compression scheme is a substitutional compression scheme
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* proposed by Abraham Lempel and Jakob Ziv in 1977. It is very simple in
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* its design, and uses no fancy bit level compression.
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*
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* This is my first attempt at an implementation of a LZ77 code/decoder.
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*
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* The principle of the LZ77 compression algorithm is to store repeated
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* occurrences of strings as references to previous occurrences of the same
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* string. The point is that the reference consumes less space than the
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* string itself, provided that the string is long enough (in this
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* implementation, the string has to be at least 4 bytes long, since the
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* minimum coded reference is 3 bytes long). Also note that the term
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* "string" refers to any kind of byte sequence (it does not have to be
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* an ASCII string, for instance).
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*
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* The coder uses a brute force approach to finding string matches in the
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* history buffer (or "sliding window", if you wish), which is very, very
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* slow. I recon the complexity is somewhere between O(n^2) and O(n^3),
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* depending on the input data.
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*
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* There is also a faster implementation that uses a large working buffer
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* in which a "jump table" is stored, which is used to quickly find
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* possible string matches (see the source code for LZ_CompressFast() for
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* more information). The faster method is an order of magnitude faster,
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* but still quite slow compared to other compression methods.
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*
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* The upside is that decompression is very fast, and the compression ratio
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* is often very good.
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*
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* The reference to a string is coded as a (length,offset) pair, where the
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* length indicates the length of the string, and the offset gives the
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* offset from the current data position. To distinguish between string
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* references and literal strings (uncompressed bytes), a string reference
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* is preceded by a marker byte, which is chosen as the least common byte
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* symbol in the input data stream (this marker byte is stored in the
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* output stream as the first byte).
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*
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* Occurrences of the marker byte in the stream are encoded as the marker
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* byte followed by a zero byte, which means that occurrences of the marker
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* byte have to be coded with two bytes.
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*
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* The lengths and offsets are coded in a variable length fashion, allowing
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* values of any magnitude (up to 4294967295 in this implementation).
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*
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* With this compression scheme, the worst case compression result is
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* (257/256)*insize + 1.
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*
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*-------------------------------------------------------------------------
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* Copyright (c) 2003-2006 Marcus Geelnard
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*
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* This software is provided 'as-is', without any express or implied
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* warranty. In no event will the authors be held liable for any damages
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* arising from the use of this software.
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*
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* Permission is granted to anyone to use this software for any purpose,
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* including commercial applications, and to alter it and redistribute it
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* freely, subject to the following restrictions:
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*
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* 1. The origin of this software must not be misrepresented; you must not
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* claim that you wrote the original software. If you use this software
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* in a product, an acknowledgment in the product documentation would
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* be appreciated but is not required.
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*
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* 2. Altered source versions must be plainly marked as such, and must not
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* be misrepresented as being the original software.
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*
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* 3. This notice may not be removed or altered from any source
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* distribution.
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*
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* Marcus Geelnard
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* marcus.geelnard at home.se
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*************************************************************************/
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/*************************************************************************
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* INTERNAL FUNCTIONS *
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*************************************************************************/
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/*************************************************************************
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* _LZ_ReadVarSize() - Read unsigned integer with variable number of
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* bytes depending on value.
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*************************************************************************/
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static int _LZ_ReadVarSize( unsigned int * x, const unsigned char * buf )
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{
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unsigned int y, b, num_bytes;
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/* Read complete value (stop when byte contains zero in 8:th bit) */
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y = 0;
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num_bytes = 0;
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do
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{
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b = (unsigned int) (*buf ++);
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y = (y << 7) | (b & 0x0000007f);
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++ num_bytes;
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}
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while( b & 0x00000080 );
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/* Store value in x */
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*x = y;
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/* Return number of bytes read */
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return num_bytes;
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}
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/*************************************************************************
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* PUBLIC FUNCTIONS *
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*************************************************************************/
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/*************************************************************************
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* LZ_Uncompress() - Uncompress a block of data using an LZ77 decoder.
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* in - Input (compressed) buffer.
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* out - Output (uncompressed) buffer. This buffer must be large
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* enough to hold the uncompressed data.
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* insize - Number of input bytes.
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*************************************************************************/
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void LZ_Uncompress( const unsigned char *in, unsigned char *out,
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unsigned int insize )
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{
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unsigned char marker, symbol;
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unsigned int i, inpos, outpos, length, offset;
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/* Do we have anything to uncompress? */
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if( insize < 1 )
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{
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return;
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}
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/* Get marker symbol from input stream */
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marker = in[ 0 ];
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inpos = 1;
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/* Main decompression loop */
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outpos = 0;
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do
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{
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symbol = in[ inpos ++ ];
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if( symbol == marker )
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{
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/* We had a marker byte */
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if( in[ inpos ] == 0 )
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{
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/* It was a single occurrence of the marker byte */
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out[ outpos ++ ] = marker;
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++ inpos;
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}
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else
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{
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/* Extract true length and offset */
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inpos += _LZ_ReadVarSize( &length, &in[ inpos ] );
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inpos += _LZ_ReadVarSize( &offset, &in[ inpos ] );
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/* Copy corresponding data from history window */
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for( i = 0; i < length; ++ i )
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{
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out[ outpos ] = out[ outpos - offset ];
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++ outpos;
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}
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}
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}
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else
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{
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/* No marker, plain copy */
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out[ outpos ++ ] = symbol;
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}
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}
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while( inpos < insize );
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}
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