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

[dak]

On 2013/02/18 02:59:58, Keith wrote:
> On Sun, 17 Feb 2013 02:07:19 -0800, mailto:address@hidden
<mailto:address@hidden>
> wrote:

> The classic error with floating point is to do math on the pair,
> something like (left .  right) + shift/3.0 , where left==right, and
> then ask is_empty().  For some compiler options, the optimizer could
> keep left+shift/3 in register while right+shift/3 was stored to
> memory.  If the register has finer precision than the memory format,
> and right+shift/3 was rounded down when stored, then is_empty() can
> return true.

This is sick enough to be right.  One can explicitly cast to the used
floating point type or assign to variables, however.  I think that the
standards allow this sort of "higher precision than warranted"
operation only for intermediate results.  With Scheme code, there is
not much of a danger since the additions will pass through the same
code path and thus get the same treatment for same values.


https://codereview.appspot.com/7310075/