Compile time tuning is available through CMake options.
Do not compile the library targeted for performance with the AOCL_ENABLE_LOG_FEATURE option.
Following options are available to enable/disable specific optimizations in respective compression methods:
Flag |
Description |
Use case |
|---|---|---|
AOCL_LZ4_MATCH_SKIP_OPT _LDS_STRAT1 (LZ4)
AOCL_LZ4_MATCH_SKIP_OPT _LDS_STRAT2 (LZ4)
SNAPPY_MATCH_SKIP_OPT (Snappy)
AOCL_ZSTD_SEARCH_SKIP_OPT (ZSTD)
|
If matches are not found for N number of bytes when parsing input data, increase the parsing step size from 1 to M and look for matches at these points only. This provides faster compression in scenarios where it is hard to find matches at the expense of compression ratio. AOCL_LZ4_MATCH_SKIP_OPT _LDS_STRAT2 does more aggressive skipping that
AOCL_LZ4_MATCH_SKIP_OPT _LDS_STRAT1 for LZ4.
[Values: ON / OFF, Defaults:
AOCL_LZ4_MATCH_SKIP_OPT _LDS_STRAT1 (OFF)
AOCL_LZ4_MATCH_SKIP_OPT _LDS_STRAT2 (OFF)
SNAPPY_MATCH_SKIP_OPT (ON)
AOCL_ZSTD_SEARCH_SKIP_OPT (ON)]
|
Files that are hard to compress |
AOCL_LZ4_NEW_PRIME _NUMBER (LZ4)
AOCL_LZ4_EXTRA_HASH _TABLE_UPDATES (LZ4)
AOCL_LZ4_HASH_BITS_USED (LZ4)
SNAPPY_HIGH_COMPRESSION (Snappy)
|
A hash table is used to keep a dictionary of matches found in the past for different byte patterns in the input. In LZ4 multiplicative hashing function is used, which takes 5 bytes of input and multiplies it with a hard-coded prime number to get the hash. In Snappy, hash value is generated using the CRC32 algorithm. AOCL_LZ4_NEW_PRIME _NUMBER: Alternate prime number found through
empirical studies is used [Values: ON / OFF (default)]
AOCL_LZ4_EXTRA_HASH _TABLE_UPDATES: When a match of length N is found,
the next comparison begins from src+N. Bytes that are skipped are not added
to hash table by default. This flag inserts some of these skipped bytes
into the hash table thus providing better compression.
[Values: ON / OFF (default)]
AOCL_LZ4_HASH_BITS_USED: Use more than 5 bytes (40 bits) when computing
hash. LOW: 41 bits, HIGH: 44 bits.
[Values: LOW / HIGH (LOW by default)]
SNAPPY_HIGH_COMPRESSION: Hash table size is doubled if input size is more than 32 KB.
[Values: ON / OFF (default)]
|
AOCL_LZ4_NEW_PRIME _NUMBER: Determine experimentally if it is useful for
your data set
AOCL_LZ4_EXTRA_HASH _TABLE_UPDATES: Better compression desired
AOCL_LZ4_HASH_BITS_USED: Better speed desired
SNAPPY_HIGH_COMPRESSION: Better compression desired
|
AOCL_LZ4_OPT_PREFETCH _BACKWARDS (LZ4)
|
Prefetch match candidates in advance [Values: ON / OFF (default)] |
Data with higher likelihood of finding matches |
AOCL_LZ4HC_DISABLE _PATTERN_ANALYSIS (LZ4HC)
|
Disable fast code path to handle repeated byte patterns such as “000000”. Faster compression when data does not have such patterns. [Values: ON (default) / OFF] |
Enable if data contains such patterns |
ENABLE_FAST_MATH |
Enable fast math optimizations [Values: ON / OFF (default)] |
Enable if application is not sensitive to floating-point numerical accuracy |
SNAPPY_ENABLE _DECOMPRESS_BRANCHLESS (Snappy)
|
Enable Snappy branchless decompression optimization. [Values: ON / OFF (default value: ON for non-GCC and OFF for GCC compiler)] |
For non-GCC compilers, disable this option if performance is less when compared to with this option. |
AOCL_COMPRESS_FAST (ZSTD) |
Enable fast compression modes that might compromise on compression ratio but provide faster compression. Supported values: ZSTD (levels 1-3).
Disabled by default.
|
Faster compression speed desired while accepting lower compression ratio. |
AOCL_ZSTD_DYN_BLOCK_SIZE (ZSTD) |
Enable ZSTD dynamic block size determination. [Values: ON / OFF (default)] |
Enable in order to improve compressibility. |
AOCL_BZIP2_HUFFMAN _ITERATIONS (BZIP2)
|
Control number of BZIP2 Huffman tables refinement iterations. Supported values: levels 1-4, default value is 3.
|
Lower values are faster but reduce compression ratio. |
AOCL_DECOMPRESS_FAST (LZ4, ZSTD & SNAPPY) |
Enable fast decompression modes that might compromise on compression speed / ratio to produce streams that decompress faster. Supported values: ZSTD (levels 1-3), Snappy (levels 1-2), and LZ4 (level 1).
Disabled by default.
|
Applications with focus on faster decompression speeds. E.g.: Applications that compress once, decompress multiple times.
|