in reply to False positive on inequality comparison

A quick and dirty but surprisingly useful trick to use when dealing with floating point issues is to use string comparison operators rather than numeric ones. Try it and see if it works.
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Re^2: False positive on inequality comparison
by Nkuvu (Priest) on Apr 06, 2009 at 17:21 UTC

    That's something I would never have thought of. But it worked perfectly. String comparison found no difference -- even when a numeric comparison did find a difference. Thanks for the idea.

[reply]

      Using string comparison on floats is dangerous, unless you don't care if the floats are actually different!

      As this shows in the last line, Perl's default stringification for floats will only show you 6 decimal places of precision, anything beyond that accuracy and you are just pretending the are the same. 

      $first = unpack 'd', pack 'b64', 
'1001110001010011100010111001000010000101000001010110011000000010';;

$second = unpack 'd', pack 'b64', 
'1010110001010011100010111001000010000101000001010110011000000010';;

printf "%f %f :> %17.17f\n", $first, $second, $first - $second;;
181.019658 181.019658 :> 0.00000000000011369

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