lzfse_tunables.h

/*
Copyright (c) 2015-2016, Apple Inc. All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:  

1.  Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2.  Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer
    in the documentation and/or other materials provided with the distribution.

3.  Neither the name of the copyright holder(s) nor the names of any contributors may be used to endorse or promote products derived
    from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

#ifndef LZFSE_TUNABLES_H
#define LZFSE_TUNABLES_H

//  Parameters controlling details of the LZ-style match search. These values
//  may be modified to fine tune compression ratio vs. encoding speed, while
//  keeping the compressed format compatible with LZFSE. Note that
//  modifying them will also change the amount of work space required by
//  the encoder. The values here are those used in the compression library
//  on iOS and OS X.

//  Number of bits for hash function to produce. Should be in the range
//  [10, 16]. Larger values reduce the number of false-positive found during
//  the match search, and expand the history table, which may allow additional
//  matches to be found, generally improving the achieved compression ratio.
//  Larger values also increase the workspace size, and make it less likely
//  that the history table will be present in cache, which reduces performance.
#define LZFSE_ENCODE_HASH_BITS 14

//  Number of positions to store for each line in the history table. May
//  be either 4 or 8. Using 8 doubles the size of the history table, which
//  increases the chance of finding matches (thus improving compression ratio),
//  but also increases the workspace size.
#define LZFSE_ENCODE_HASH_WIDTH 4

//  Match length in bytes to cause immediate emission. Generally speaking,
//  LZFSE maintains multiple candidate matches and waits to decide which match
//  to emit until more information is available. When a match exceeds this
//  threshold, it is emitted immediately. Thus, smaller values may give
//  somewhat better performance, and larger values may give somewhat better
//  compression ratios.
#define LZFSE_ENCODE_GOOD_MATCH 40

//  When the source buffer is very small, LZFSE doesn't compress as well as
//  some simpler algorithms. To maintain reasonable compression for these
//  cases, we transition to use LZVN instead if the size of the source buffer
//  is below this threshold.
#define LZFSE_ENCODE_LZVN_THRESHOLD 4096

#endif // LZFSE_TUNABLES_H