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.\" ========================================================================
.\"
.IX Title "Bloom::Filter 3pm"
.TH Bloom::Filter 3pm "2021-01-09" "perl v5.32.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
Bloom::Filter \- Sample Perl Bloom filter implementation
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
A Bloom filter is a probabilistic algorithm for doing existence tests
in less memory than a full list of keys would require.  The tradeoff to
using Bloom filters is a certain configurable risk of false positives.
This module implements a simple Bloom filter with configurable capacity
and false positive rate. Bloom filters were first described in a 1970
paper by Burton Bloom, see <http://portal.acm.org/citation.cfm?id=362692&dl=ACM&coll=portal>.
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&        use Bloom::Filter
\&
\&        my $bf = Bloom::Filter\->new( capacity => 10, error_rate => .001 );
\&
\&        $bf\->add( @keys );
\&
\&        while ( <> ) {
\&                chomp;
\&                print "Found $_\en" if $bf\->check( $_ );
\&        }
.Ve
.SH "CONSTRUCTORS"
.IX Header "CONSTRUCTORS"
.ie n .IP "new %PARAMS" 4
.el .IP "new \f(CW%PARAMS\fR" 4
.IX Item "new %PARAMS"
Create a brand new instance.  Allowable params are \f(CW\*(C`error_rate\*(C'\fR, \f(CW\*(C`capacity\*(C'\fR.
.IP "init" 4
.IX Item "init"
Calculates the best number of hash functions and optimum filter length,
creates some random salts, and generates a blank bit vector.  Called
automatically by constructor.
.SH "ACCESSORS"
.IX Header "ACCESSORS"
.IP "capacity" 4
.IX Item "capacity"
Returns the total capacity of the Bloom filter
.IP "error_rate" 4
.IX Item "error_rate"
Returns the configured maximum error rate
.IP "length" 4
.IX Item "length"
Returns the length of the Bloom filter in bits
.IP "key_count" 4
.IX Item "key_count"
Returns the number of items currently stored in the filter
.IP "on_bits" 4
.IX Item "on_bits"
Returns the number of 'on' bits in the filter
.IP "salts" 4
.IX Item "salts"
Returns the list of salts used to create the hash functions
.SH "PUBLIC METHODS"
.IX Header "PUBLIC METHODS"
.ie n .IP "add @KEYS" 4
.el .IP "add \f(CW@KEYS\fR" 4
.IX Item "add @KEYS"
Adds the list of keys to the filter.   Will fail, return \f(CW\*(C`undef\*(C'\fR and complain
if the number of keys in the filter exceeds the configured capacity.
.ie n .IP "check @KEYS" 4
.el .IP "check \f(CW@KEYS\fR" 4
.IX Item "check @KEYS"
Checks the provided key list against the Bloom filter,
and returns a list of equivalent length, with true or
false values depending on whether there was a match.
.SH "INTERNAL METHODS"
.IX Header "INTERNAL METHODS"
.IP "_calculate_shortest_filter_length \s-1CAPACITY ERR_RATE\s0" 4
.IX Item "_calculate_shortest_filter_length CAPACITY ERR_RATE"
Given a desired error rate and maximum capacity, returns the optimum
combination of vector length (in bits) and number of hash functions
to use in building the filter, where \*(L"optimum\*(R" means shortest vector length.
.IP "_get_cells \s-1KEY\s0" 4
.IX Item "_get_cells KEY"
Given a key, hashes it using the list of salts and returns
an array of cell indexes corresponding to the key.
.SH "AUTHOR"
.IX Header "AUTHOR"
Originally written by Maciej Ceglowski <maciej@ceglowski.com>.
Currently maintained by Grzegorz Rożniecki <xaerxess@gmail.com>.
.SH "CONTRIBUTORS"
.IX Header "CONTRIBUTORS"
Dmitriy Ryaboy <dmitriy.ryaboy@ask.com> (big speedup in February 2007, thanks!)
.SH "COPYRIGHT AND LICENSE"
.IX Header "COPYRIGHT AND LICENSE"
(c) 2004 Maciej Ceglowski
.PP
This is free software, distributed under version 2
of the \s-1GNU\s0 Public License (\s-1GPL\s0).