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#!perl
# Note: This script is a CLI for Riap function /App/BloomUtils/bloom_filter_calculator
# and generated automatically using Perinci::CmdLine::Gen version 0.496
our $AUTHORITY = 'cpan:PERLANCAR'; # AUTHORITY
our $DATE = '2020-05-24'; # DATE
our $DIST = 'App-BloomUtils'; # DIST
our $VERSION = '0.007'; # VERSION
use 5.010001;
use strict;
use warnings;
use Log::ger;
use Perinci::CmdLine::Any;
my $cmdline = Perinci::CmdLine::Any->new(
    url => "/App/BloomUtils/bloom_filter_calculator",
    program_name => "bloom-filter-calculator",
    log => 1,
    read_config => 0,
    read_env => 0,
);
$cmdline->run;
# ABSTRACT: Help calculate num_bits (m) and num_hashes (k)
# PODNAME: bloom-filter-calculator
__END__
HideShow 244 lines of Pod
=pod
=encoding UTF-8
=head1 NAME
bloom-filter-calculator - Help calculate num_bits (m) and num_hashes (k)
=head1 VERSION
This document describes version 0.007 of bloom-filter-calculator (from Perl distribution App-BloomUtils), released on 2020-05-24.
=head1 SYNOPSIS
Usage:
 % bloom-filter-calculator [--debug] [--false-positive-rate=s]
     [--format=name] [--fp-rate=s] [--json] [-k=s] [--log-level=level]
     [-m=s] [--(no)naked-res] [--num-bits=s]
     [--num-hashes-to-bits-per-item-ratio=s] [--num-hashes=s] [-p=s]
     [--page-result[=program]] [--quiet] [--trace] [--verbose] <num_items>
=head1 DESCRIPTION
You supply lines of text from STDIN and it will output the bloom filter bits on
STDOUT. You can also customize C<num_bits> (C<m>) and C<num_hashes> (C<k>), or, more
easily, C<num_items> and C<fp_rate>. Some rules of thumb to remember:
=over
=item * One byte per item in the input set gives about a 2% false positive rate. So if
you expect two have 1024 elements, create a 1KB bloom filter with about 2%
false positive rate. For other false positive rates:
10%    -  4.8 bits per item
 1%    -  9.6 bits per item
 0.1%  - 14.4 bits per item
 0.01% - 19.2 bits per item
=item * Optimal number of hash functions is 0.7 times number of bits per item. Note
that the number of hashes dominate performance. If you want higher
performance, pick a smaller number of hashes. But for most cases, use the the
optimal number of hash functions.
=item * What is an acceptable false positive rate? This depends on your needs. 1% (1
in 100) or 0.1% (1 in 1,000) is a good start. If you want to make sure that
user's chosen password is not in a known wordlist, a higher false positive
rates will annoy your user more by rejecting her password more often, while
lower false positive rates will require a higher memory usage.
=back
Ref: https://corte.si/posts/code/bloom-filter-rules-of-thumb/index.html
B<FAQ>
=over
=item * Why does two different false positive rates (e.g. 1% and 0.1%) give the same bloom filter size?
The parameter C<m> is rounded upwards to the nearest power of 2 (e.g. 1024*8
bits becomes 1024*8 bits but 1025*8 becomes 2048*8 bits), so sometimes two
false positive rates with different C<m> get rounded to the same value of C<m>.
Use the C<bloom_filter_calculator> routine to see the C<actual_m> and C<actual_p>
(actual false-positive rate).
=back
=head1 OPTIONS
C<*> marks required options.
=head2 Main options
=over
=item B<--false-positive-rate>=I<s>, B<-p>, B<--fp-rate>
Default value:
 0.02
=item B<--num-bits>=I<s>, B<-m>
Number of bits to set for the bloom filter.
=item B<--num-hashes-to-bits-per-item-ratio>=I<s>
0.7 (the default) is optimal.
=item B<--num-hashes>=I<s>, B<-k>
=item B<--num-items>=I<s>*, B<-n>
Expected number of items to add to bloom filter.
=back
=head2 Logging options
=over
=item B<--debug>
Shortcut for --log-level=debug.
=item B<--log-level>=I<s>
Set log level.
=item B<--quiet>
Shortcut for --log-level=error.
=item B<--trace>
Shortcut for --log-level=trace.
=item B<--verbose>
Shortcut for --log-level=info.
=back
=head2 Output options
=over
=item B<--format>=I<s>
Choose output format, e.g. json, text.
Default value:
 undef
=item B<--json>
Set output format to json.
=item B<--naked-res>
When outputing as JSON, strip result envelope.
Default value:
 0
By default, when outputing as JSON, the full enveloped result is returned, e.g.:
    [200,"OK",[1,2,3],{"func.extra"=>4}]
The reason is so you can get the status (1st element), status message (2nd
element) as well as result metadata/extra result (4th element) instead of just
the result (3rd element). However, sometimes you want just the result, e.g. when
you want to pipe the result for more post-processing. In this case you can use
`--naked-res` so you just get:
    [1,2,3]
=item B<--page-result>
Filter output through a pager.
=back
=head2 Other options
=over
=item B<--help>, B<-h>, B<-?>
Display help message and exit.
=item B<--version>, B<-v>
Display program's version and exit.
=back
=head1 COMPLETION
This script has shell tab completion capability with support for several
shells.
=head2 bash
To activate bash completion for this script, put:
 complete -C bloom-filter-calculator bloom-filter-calculator
in your bash startup (e.g. F<~/.bashrc>). Your next shell session will then
recognize tab completion for the command. Or, you can also directly execute the
line above in your shell to activate immediately.
It is recommended, however, that you install modules using L<cpanm-shcompgen>
which can activate shell completion for scripts immediately.
=head2 tcsh
To activate tcsh completion for this script, put:
 complete bloom-filter-calculator 'p/*/`bloom-filter-calculator`/'
in your tcsh startup (e.g. F<~/.tcshrc>). Your next shell session will then
recognize tab completion for the command. Or, you can also directly execute the
line above in your shell to activate immediately.
It is also recommended to install L<shcompgen> (see above).
=head2 other shells
For fish and zsh, install L<shcompgen> as described above.
=head1 HOMEPAGE
Please visit the project's homepage at L<https://metacpan.org/release/App-BloomUtils>.
=head1 SOURCE
Source repository is at L<https://github.com/perlancar/perl-App-BloomUtils>.
=head1 BUGS
Please report any bugs or feature requests on the bugtracker website L<https://rt.cpan.org/Public/Dist/Display.html?Name=App-BloomUtils>
When submitting a bug or request, please include a test-file or a
patch to an existing test-file that illustrates the bug or desired
feature.
=head1 AUTHOR
perlancar <perlancar@cpan.org>
=head1 COPYRIGHT AND LICENSE
This software is copyright (c) 2020, 2018 by perlancar@cpan.org.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
=cut