qap

Qap, a quick parser/matcher optimized for string and buffer patterns (<= 255 bytes).

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Qap, a Quick Parser

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  • Qap is a quick parser for string or buffer patterns.
  • It is optimized for using with pattern strings <= 255 bytes.
  • Better results are achieved with long and sparse patterns.
  • It is an implementation of QuickSearch algorithm.

Main features

Given a m-length pattern and n-length data and σ-length alphabet ( σ = 256 ):

  • simplification of the Boyer-Moore algorithm ( see Bop ).
  • uses only a bad-character shift table.
  • preprocessing phase in O(m+σ) time and O(σ) space complexity.
  • searching phase in O(m*n) time complexity.
  • very fast in practice for short patterns and large alphabets.

See Lecroq for reference and also Bop, a Boyer-Moore parser.

Install

$ npm install qap [-g]

require:

var Qap = require( 'qap' );

Run Tests

$cd qap/
$npm test

Run Benchmarks

$ cd qap/
$ npm run-script bench

Constructor

Create an instance with a Buffer or String pattern.

Qap( Buffer || String pattern )
// or
neq Qap( Buffer || String pattern )

Methods

List all pattern occurrences into a String or Buffer data. It returns a new array of indexes, or populates an array passed as the last argument to parse method.

// slower with String
Qap#parse( String data [, Number startFromIndex [, Number limitResultsTo [, Array array ] ] ] ) : Array

// faster with Buffer
Qap#parse( Buffer data [, Number startFromIndex [, Number limitResultsTo [, Array array ] ] ] ) : Array

Change the pattern :

Qap#set( Buffer || String pattern ) : Buffer

Usage Example

var log = console.log
    , assert = require( 'assert' )
    , Qap = require( 'qap' )
    , pattern = 'hellofolks\r\n\r\n'
    , text = 'hehe' + pattern +'loremipsumhellofolks\r\n' + pattern
    , bresult = null
    ;

// create an instance and parse the pattern
var qap = Qap( pattern )
    // parse data from beginning
    , results = qap.parse( text )
    ;

// set a new Buffer pattern
qap.set( new Buffer( pattern ) );

// parse data uffer instead of a String
bresults = qap.parse( new Buffer( text ) );

// parser results ( starting indexes ) [ 4, 40 ]
log( results, bresults );

// results are the same
assert.deepEqual( results, bresults );

Benchmark for a small pattern ( length <= 255 bytes )

Parser uses a Buffer 256-bytes long to build the shifting table, then:

  • Pattern parsing / table creation space and time complexity is O(σ).
  • Very low memory footprint.
  • Ultra fast to preprocess pattern ( = table creation ).
  $ node bench/small-pattern-data-rate

for default it:

  • uses a pattern string of 57 bytes/chars
  • builds a data buffer of 700 MB in memory
  • uses a redundancy/distance factor for pattern strings equal to 2. The bigger the value, the lesser are occurrences of pattern string into the text buffer.

Custom Usage:

  # with [testBufferSizeInMB] [distanceFactor] [aStringPattern]
  $ node bench/small-pattern-data-rate.js 700 4 "that'sallfolks"

Benchmark for a big pattern ( length > 255 bytes )

Parser uses one Array to build the shifting table for a big pattern, then:

  • table has a size of 256 elements, every element is an integer value that could be between 0 and the pattern length.
  • Fast to preprocess pattern ( = table creation ).
  • Low memory footprint
  $ node bench/big-pattern-data-rate
  • it uses a pattern size of 20MB
  • builds a data buffer of 300MB copying pattern 12 times

See bench dir.

MIT License

Copyright (c) 2012 < Guglielmo Ferri : 44gatti@gmail.com >

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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