Geometry Boost List: Re: [geometry] warning: comparing floating point with == or != is unsafe

Subject: Re: [geometry] warning: comparing floating point with == or != is unsafe
From: Barend Gehrels (barend_at_[hidden])
Date: 2013-06-07 14:18:21

Hi,

On 7-6-2013 4:46, Adam Wulkiewicz wrote:
> Mateusz Loskot wrote:
>> On 7 June 2013 01:36, Adam Wulkiewicz <adam.wulkiewicz_at_[hidden]> wrote:
>>>
>>> Ah, I've forgotten to handle this after porting it from the old 
>>> version.
>>> Thanks for digging this up. Yes, there should probably be comparison 
>>> with
>>> std::numeric_limits<coordinate_type>::epsilon().
>>
>> You may try GCC/clang with -Wfloat-equal, there is a few more, but those
>> need to be addressed individually, I think.
>>
>> So, we may discuss unobvious cases.
>>
>
> In the Index there are comparisons in:
>
> /boost/geometry/index/detail/rtree/visitors/insert.hpp:70
> /boost/geometry/index/detail/rtree/linear/redistribute_elements.hpp:326
> /boost/geometry/index/detail/rtree/quadratic/redistribute_elements.hpp:189 
>
> /boost/geometry/index/detail/rtree/rstar/redistribute_elements.hpp:93
> /boost/geometry/index/detail/rtree/rstar/choose_next_node.hpp:112
>
> but they're ok.
>
> And I've detected also the one in:
>
> /boost/geometry/util/math.hpp:54 

That one first compares with == indeed. If that is true, it returns true 
(whatever the epsilon is, if == returns true, it will always return 
true). If == is false, it does a more sophisticated comparison, still 
intended to be replaced by some Boost utility. See the comments. There 
are still some issues with this (not exactly with this, but with FP in 
general).

Regards, Barend