File Coverage

blib/lib/Photography/EV.pm

Criterion	Covered	Total	%
statement	49	59	83.0
branch	15	26	57.6
condition	3	3	100.0
subroutine	13	13	100.0
pod	3	3	100.0
total	83	104	79.8

package Photography::EV 0.07 {

  use strict;
  use warnings;
  use 5.020000;
  use experimental 'signatures';
  use base qw( Exporter );
  BEGIN {
    eval q{
      use POSIX qw( pow );
    };
    if($@)
    {
      *pow = sub ($x, $exponent)
      {
        my $value = 1;
        for(1..$exponent)
        {
          $value *= $x;
        }
        $value;
      }
    }
  }

  our @EXPORT_OK = qw( ev aperture shutter_speed );
  our @EXPORT = @EXPORT_OK;

# ABSTRACT: Calculate exposure value (EV)


  sub _round :prototype($)
  {
    return $_[0] ? int($_[0] + $_[0]/abs($_[0]*2)) : 0;
  }

  sub _log2 :prototype($)
  {
    return log($_[0])/log(2);
  }

  # returns the closest value in @$list to $exact
  # returns undef if @$list is empty
  sub _closest :prototype($$)
  {
    my($exact, $list) = @_;
    my $answer;
    my $diff;
    for(@$list)
    {
      my $maybe = abs($_ - $exact);
      if((!defined $answer) || $maybe < $diff)
      {
        $answer = $_;
        $diff = $maybe;
      }
    }
    $answer;
  }

  my @apertures = qw(
    1.0
    1.4
    2.8
    4.0
    5.6
    8.0
    11
    16
    22
    32
    45
    64
  );

  my @times = (
    (map { $_ * 60 } qw( 32 16 8 4 2 )),
    (                qw( 60 30 15 8 4 2 1)),
    (map { 1 / $_  } qw( 2 4 8 15 30 125 250 500 1000 2000 4000 8000 ))
  );


  sub ev ($aperture, $time)
  {
    return _round _log2 $aperture*$aperture/$time;
  }


  sub aperture ($ev, $time, $apertures = \@apertures )
  {
    return _closest sqrt pow(2, $ev)*$time, $apertures;
  }


  sub shutter_speed ($ev, $aperture, $times = \@times )
  {
    return _closest $aperture*$aperture/pow(2, $ev), $times;
  }

}

1;

__END__