Re: Standardizes use of empty extents in pure heights and skylines. (issue 7310075)

[Janek Warchoł]

Hi,

On Wed, Mar 13, 2013 at 10:44 AM,  <address@hidden> wrote:
>
> "address@hidden" <address@hidden> writes:
>> The concern before was a comment about numerical inaccuracy, but after
>> having tested the patch, this seems not to be an issue.
>
> Like Keith pointed out, it could become one if more than one operation
> is done before storing the result, and/or there are different code paths
> for doing the operations to the different ends of an interval.
>
> If left and right have equal values to start with, C++ is still not
> required to have left and right receive the same value after
>
> left = left*factor + offset;
> right = right*factor + offset;
>
> That's totally sick.  It may be worth using GCC compiler options to
> disallow extended precision for intermediate results and/or the choice
> to store intermediates with less than full precision and try to retain
> some kind of deterministic behavior that way.

attached is a patch that turns your explanations into a comment and
contains some explanatory text for commit message.  You may want to
double-check whether i got everything right.

thanks,
Janek

0002-add-a-comment-explaining-numerical-accuracy-issues.patch
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