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Re: Rounding of a number...

by Gilimanjaro (Hermit)
on Dec 27, 2004 at 12:00 UTC ( #417534=note: print w/replies, xml ) Need Help??

in reply to Rounding of a number...

In the spirit of TIMTOWDI:
sprint("%5.2f",$yearlyamount/52 - 0.005)

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Re^2: Rounding of a number...
by Anonymous Monk on Dec 27, 2004 at 13:26 UTC
    For my machine, it will give the wrong answer for any time $yearlyamount equals k * 13, for k at least 9. This is because 52 is 4 * 13, and hence the division by 52 gives the exact answer, and subtracting 0.005 (which cannot be represented exactly in binary) from it causes %f to round it down to the next decimal. For instance, 117 / 52 - 0.005, on my computer with my Perl (5.8.6, with longdoubles and 64bitints) is about 2.244999999999999999895916591441391574335284531116485595703125. Just a tiny, tiny bit below 2.245, but that's enough to give the answer 2.24, instead of 2.25.

    Doing arithmetic with reals is very tricky, and it's therefore better to use a good module. for instance, with its floor method.

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[choroba]: but undef %hash and %hash = () both work, too, but the first one keeps the memory allocated, while the latter makes it available for other parts of the program.
[choroba]: iirc
[perldigious]: karlgoethebier: Well it is a pretty old and complicated (for me) bit of code I wrote (poorly by my current standards), so I'm expecting everything to break when I add the scoping and find out what else is undesireably scope changed. :-)
[perldigious]: Ah, thanks choroba, that sort of thing was precisely what I was wondering when I asked.
[perldigious]: I didn't want to tie up memory unecessarily basically, I wanted to "delete" it specifically to free it up, and wasn't sure I was even accomplishing that.
[stevieb]: perldigious You should start by writing some unit tests. That'll ensure current functionality doesn't break with changes.
[choroba]: unit tests++

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