Re: [PATCH] swsusp: simpler calculation of number of pages in PBE list

Rafael J. Wysocki
2005-07-29T21:53:38Z

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On Friday, 29 of July 2005 23:14, Michal Schmidt wrote:
> Rafael J. Wysocki wrote:
> > On Friday, 29 of July 2005 21:46, Michal Schmidt wrote:
> >
> >>The function calc_nr uses an iterative algorithm to calculate the number
> >>of pages needed for the image and the pagedir. Exactly the same result
> >>can be obtained with a one-line expression.
> >
> >
> > Could you please post the proof?
> >
> > Rafael
>
> OK, attached is a proof-by-brute-force program. It compares the results
> of the original function and the simplified one.
>
> This is its output:
>
> $ ./calc_nr2
> checked 0 ...
> checked 100000000 ...
> checked 200000000 ...
> checked 300000000 ...
> checked 400000000 ...
> checked 500000000 ...
> checked 600000000 ...
> checked 700000000 ...
> checked 800000000 ...
> checked 900000000 ...
> checked 1000000000 ...
> checked 1100000000 ...
> checked 1200000000 ...
> checked 1300000000 ...
> checked 1400000000 ...
> checked 1500000000 ...
> checked 1600000000 ...
> checked 1700000000 ...
> checked 1800000000 ...
> checked 1900000000 ...
> checked 2000000000 ...
> checked 2100000000 ...
> First difference at 2130706433: -2147483646 x -2147483647
>
> It means that the two functions give the same results for sensible
> values of the input argument.
> They results only differ when they overflow into negative values. At
> this point both of the results are useless.

Thanks, fine. :-)

Greets,
Rafael

--
- Would you tell me, please, which way I ought to go from here?
- That depends a good deal on where you want to get to.
-- Lewis Carroll "Alice's Adventures in Wonderland"