Dear Monks, I have currently a set of values for weekdays, that is stored as integer. To clarify here are example binary values:
Mon = 0b0000001 = 1
Tue = 0b0000010 = 2
Mon to Fri = 0b0011111 = 31
Sat to Sun = 0b1100000 = 96
I need to know how many days of running two sets of data have in common. This is a simple task, however I got stuck in a vicious circle between simplicity and performance. I st up five test functions and compared their speed. It did not surprise me much, that the fastes way is a bitwise evaluation. But if I ran through all days with a loop, the function is a lot slower. Can anyone suggest a better way to approach this? Please find the current code below. 
sub test4 {

  my ( $iDays, $iCmp ) = @_;

  my $iRes = 0;
  for ( 1, 2, 4, 8, 16, 32, 64 ){ 
    if ( $iDays & $iCmp & $_ ){
      $iRes++;
    }
  }

  return $iRes;
}

sub test5 {

  my ( $iDays, $iCmp ) = @_;

  my $iRes = 0;
  $iRes++ if ( $iDays &  $iCmp &  1 );
  $iRes++ if ( $iDays &  $iCmp &  2 );
  $iRes++ if ( $iDays &  $iCmp &  4 );
  $iRes++ if ( $iDays &  $iCmp &  8 );
  $iRes++ if ( $iDays &  $iCmp & 16 );
  $iRes++ if ( $iDays &  $iCmp & 32 );
  $iRes++ if ( $iDays &  $iCmp & 64 );

  return $iRes;
}

cmpthese($count, {
  'Test4' => sub { test4( int ( rand(127) ), int( rand(127) ) ) },
  'Test5' => sub { test5( int ( rand(127) ), int( rand(127) ) ) }
});

__DATA__
          Rate Test4 Test5
Test4 162690/s    --  -46%
Test5 300000/s   84%    --

[download]
The performance lost by the loop is quite steep, but the code nicer.

Cheers,
PerlingTheUK

In reply to Loops loosing Performance by PerlingTheUK

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