Update

Author: emmanuel-marty

README.md

@@ -3,29 +3,19 @@ lz4ultra -- Optimal LZ4 packer with faster decompression
 
 lz4ultra is a command-line optimal compression utility that produces compressed files in the [lz4](https://github.com/lz4/lz4) format created by Yann Collet.
 
-The tool creates optimally compressed files, like lz4 in optimal compression mode ("lz4hc"), smallLZ4, blz4 and lz4x. The files created with lz4ultra decompress faster.
+The tool creates optimally compressed files, like lz4 in optimal compression mode ("lz4hc"), smallLZ4, blz4 and lz4x.
 
-lz4ultra beats lz4 1.9.1 --12 --favor-decSpeed in both size and decompression speed. With enwik9 (1,000,000,000 bytes):
+With enwik9 (1,000,000,000 bytes):
 
                                       Compr.size    Tokens      Decomp.time (μs, Core i7-6700)
-    lz4 1.9.1 --12 (favor ratio)      371,680,440   95,708,169  345,272
-    smalLZ4 1.3                       371,680,328   93,172,985  343,571
-    lz4ultra 1.1.3 (favor ratio)      371,687,509   85,910,002  342,159
-    lz4 1.9.1 --12 --favor-decSpeed   376,408,347   92,105,212  304,911
-    lz4ultra 1.1.3 --favor-decSpeed   376,118,380   88,521,891  289,355 <--------------
+    lz4 1.9.2 -12 (favor ratio)       372,443,347   95,698,349  505,804
+    smalLZ4 1.5 -9                    371,680,328   93,172,985  348,018
+    lz4ultra 1.3.0 (favor ratio)      371,680,323   93,165,899  347,936
+    lz4 1.9.2 -12 --favor-decSpeed    377,175,400   92,080,802  457,141
+    lz4ultra 1.3.0 --favor-decSpeed   376,118,079   88,521,993  296,972
 
 The produced files are meant to be decompressed with the lz4 tool and library. While lz4ultra includes a decompressor, it is mostly meant to verify the output of the compressor and isn't as optimized as Yann Collet's lz4 proper.
 
-lz4ultra works by performing the usual optimal compression (using a suffix array), and then applying a forward peephole optimization pass, that breaks ties (sequences of compression commands that result in an identical number of bytes added to the compressed data), in favor of outputting less commands.
-
-In other words, it will go over the compressed data before it is flattened into the output bytestream, and possibly replace match->match and match->literal sequences by a literal->match or just literal sequences, if the output size is unchanged.
-
-Everything else being equal, having less commands speeds up decompression as the decompressor is required to do less mode switches.
-
-The peephole optimizer is located in src/shrink.c, as lz4ultra_optimize_command_count(). This pass is extremely fast and cache-friendly as it just goes over the compressed data once. The logic isn't tied to compressing with a suffix array, it can be adapted to any compressor.
-
-lz4ultra is an offshoot of the [lzsa](https://github.com/emmanuel-marty/lzsa) compressor as we thought it would be interesting to the wider compression community, to users of LZ4 that compress data once and require the fastest decompression time without a trade-off in compression ratio, and also to retrocomputing developers as this will speed decompression up further on 8/16-bit systems.
-
-The tool defaults to 4 Mb blocks with inter-block dependencies but can be configured to output all of the LZ4 block sizes (64 Kb to 4 Mb) and to compress independent blocks, using command-line switches.
+The tool defaults to 4 Mb blocks with inter-block dependencies but can be configured to output all of the LZ4 block sizes (64 Kb to 4 Mb), to use the LZ4 8 Mb blocks legacy encoding, and to compress independent blocks, using command-line switches.
 
 lz4ultra is developed by Emmanuel Marty with the help of spke.