in reply to Re^2: False positive on inequality comparison
in thread False positive on inequality comparison
Can I suggest that you dump each value to a file along with some natural identifier (line number or cell ID), using:
print unpack 'b64', pack 'd', $float;; 1011110110001011101100101110110101100111111000110111101000000011
Do this immediately after reading it into your script to ensure the minimum possibility of 'internal influences'. Then, when you encounter unexpected/unexplainable differences, dump both values in the same form, along with their original identifiers.
I can't offer an explanation for how or why what you are seeing could happen, but I have seen some weirdness in Perl's internal handling of floats in the past. Dumping bit patterns is surest way I know of inspecting what is actually there.
That said, you can still be fooled, as IEEE allow for the possibility of denormalised representations. That is, the bit patterns can be different but represent (exactly) the same values. Kind of like binary equivalent of 10e-6 vs. 1e-5.
Anyway, if you can track what differences are being perceived, then you may be able to backtrack to where they arise. And if you can do that, an explanation of why may be obvious or forthcoming.
Good luck.
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Re^4: False positive on inequality comparison
by Nkuvu (Priest) on Apr 06, 2009 at 18:08 UTC | |
by BrowserUk (Patriarch) on Apr 06, 2009 at 19:19 UTC |