bc-zip

Bicriteria Compressor

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Usage

The executable is invoked with the following syntax:

./bc-zip command <command-specific options>

The most interesting commands are the following:

There are also two commands, namely encoders and gens, which we will illustrate later in this document.

bit-optimal

We report the most important options (bold options are compulsory). For others, have a look at the command-line help (just type bc-zip bit-optimal to show the help).

Option Meaning
-i file File to be compressed. Can also be specified by the first positional argument.
-o file Filename of compressed output. Can also be specified by the second positional argument.
-e encoder Integer encoder used in compression. A list of all supported encoders can be retrieved by invoking the bc-zip command “encoders”. We suggest to pick one among soda09_16 (succinct, relatively slow at decompression) and hybrid-16 (less succinct, very fast decompression speeds).
-b bucket Logically splits the input file into blocks of bucket megabytes, compresses them individually and then concatenate them to obtain the final compressed file. Lowers compression time at the expense of optimality and, thus, compression ratio.
-z Shows a progress bar while compressing.

Examples:

./bc-zip bit-optimal input output.lzo -e hybrid-16 -b 64

Compress file input into output.lzo, using the fast encoder hybrid-16, with buckets of 64 megabytes.

./bc-zip bit-optimal input output.lzo -e soda09_16 -z

Optimally compress file input into output.lzo, using the succinct encoder soda09_16.

compress

Compress implements “bicriteria” compression. In order to evaluate decompression times, a target file encoding the decompression time model for the target machine (that is, the machine in which decompression will take place) is required. Have a look at section Target files for more informations about this matter.

In the following we illustrate the most important options (bold options are compulsory).

Option Meaning
-i file File to be compressed. Can also be specified by the first positional argument.
-e encoder Integer encoder used in compression. A list of all supported encoders can be retrieved by invoking the bc-zip command “encoders”. We suggest to pick one among soda09_16 (succinct, relatively slow at decompression) and hybrid-16 (less succinct, very fast decompression speeds).
-t target Specify the target machine model file, as obtained by the calibrator tool (see the section about the calibrator for further informations), WITHOUT the .tgt suffix. That is, if the model is names X.tgt, then just pass X to this option.
-b bound Specify the compression bound. If the bound has the form XK/M, then the compression size will be at most X kilobytes/megabytes and the decompression time minimized. If the bound has the form Xm/s, then the decompression time will be at most X milliseconds/seconds (according to the target model specified with option -t ) and compressed size minimized. Multiple bounds can be specified by separating different bounds with a comma: in this case the file will be compressed multiple times, once for each bound.
-l level Specify a compression level (float in range [0,1]), which might be in compression space or decompression time. A compression level is a “relative” way of setting bounds. A level in the form XS (such as 0.5S) defines a bound on the compression space. It means that, if the most space-succinct compressed file for the input file has space S_1, and the compressed file with the highest decompression speed has space S_2 (with S_1 < S_2), then the level specifies a bound on compressed space equal to S_1 + X * (S_2 - S_1). In other words, compressing a file with level 0S is the same as compressing the file with the bit-optimal command, while compressing a file with level 1S instructs the compressor to obtain the decompression time-optimal compression file. Linearly increasing the level increases linearly the compressed space of the final parsing. A level in the form XT (such as 0.2T) similarly defines a bound on the decompression time, so a level of 0T obtains the compression with the lowest decompression time, while a level of 1T obtains the most succinct compressed file. A level of 0.5T has a decompression time which is a mean of the decompression time of the most succinct compressed file and the decompression time of the compressed file with the highest decompression speed. Multiple levels can be specified by separating different bounds with a comma: in this case the file will be compressed multiple times, once for each level.
-z Shows a progress bar while compressing.

At least one among -b or -l must be selected. The output file name is a combination of the input file name and the compression options specified.

Examples

Suppose you have a file input.txt to be compressed and a target file smartphone.tgt, which models the decompression time of a compressed file on a particular smartphone. Suppose the most succinct compressed file has a decompression time of 600 msec (with encoder hybrid-16) and takes 200MB, while the fastest compressed file is decompressed in 300msec (also with encoder hybrid-16) and takes 400MB of space. Then:

./bc-zip compress input.txt -e hybrid-16 -t smartphone -b 300M -z

Compress file input.txt with encoder hybrid-16, obtaining the fastest compressed file which is not greater than 300 megabytes (300 * 220 bytes), showing a progress bar during the process. The compressed file is input.txt#hybrid-16#300MB.lzo.

./bc-zip compress input.txt -e soda09_16 -t smartphone -b 300M,400m

Compress file input.txt two times with encoder soda09_16: the first time with a bound of 300MB (300 * 220 bytes) in space, saving in input.txt#soda09_16#300MB.lzo; the second with a time bound of 400 msecs (according to model smartphone.tgt, stored in the calling directory), saving in input.txt#soda09_16#400msec.lzo

./bc-zip compress input.txt -e hybrid-16 -t smartphone -l 0.5T,0.1T,0.1S -b 300M

Compress file input.txt four times:

decompress

Usage: bc-zip decompress input_file output_file

Example

./bc-zip decompress compressed.lzo original

Decompress file compressed.lzo into file original.