Date: Sun, 11 Jul 2004 11:38:17 -0700 (PDT) From: "Bruce R. Montague" <brucem@mail.cruzio.com> To: freebsd-hackers@freebsd.org Cc: marck@rinet.ru Subject: Re: gcc strangeness Message-ID: <200407111838.i6BIcHku000792@mail.cruzio.com>
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Hi, re:
>one of my friends has raisen very strange issue regarding gcc rounding:
> printf("%f %.3f %d\n", a*100, a*100, (int)(a*100));
>
> 9.999999 10.000 9
Hasty unresearched guess:
If you print with a large fp fmt (say 22.18)
you will get a better idea of the value:
9.999999403953552246 10.000 9
The "%.3f" says to round upward to inf after 3 decimal
places, so "9.9999" is rounded to "10.000".
The "%f" defaults to round up after 6 decimal places,
so "9.9999994" is rounded to ""9.999999".
Everything is working.
There are a lot of subtleties in floating-point
printf(). Printing binary values out and reading them
back accurately can be a non-trivial exercise.
- bruce
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