[cfe-dev] [libcxx/test] Puzzling floating point behaviour

[Edward Meewis]

On 10-12-11 5:34, Eli Friedman wrote:
> On Fri, Dec 9, 2011 at 8:23 PM, Edward Meewis
> <ed at extraordinarymachine.nl>  wrote:
>> On 10-12-11 1:34, Eli Friedman wrote:
>>>
>>> On Fri, Dec 9, 2011 at 7:58 AM, Edward Meewis
>>> <ed at extraordinarymachine.nl>    wrote:
>>>>
>>>> <snip>
>>>>
>>>>
>>>> I'm guessing long doubles get demoted somewhere. Does anyone have an
>>>> idea what the problem may be?
>>>
>>> I'm not getting quite the same results as you, but your testcase isn't
>>> really testing what you want to test: std::exp is not the same as
>>> ::exp.
>>>
>>> -Eli
>>
>> Thanks, Eli, that's probably a big clue, but I don't get it. This is
>> probably a stupid question, but can you explain? I would expect all exp's to
>> be in std::. What's the difference?
>
> std::exp is the properly overloaded exp defined by the C++ standard.
> ::exp isn't overloaded, so it loses precision.
>
> -Eli
I am certainly not convinced that things are working properly. The 
attached program and test script tests 8 cases, all compiled with fresh 
clang++ and fresh libc++:

library    WITH_NS_STD    WITH_EXP_OVERLOADED  Result
-------------------------------------------------------
libc++     no             no                   d incorrect, dx1 correct
libc++     no             yes                  d, dx1 correct
libc++     yes            no                   d, dx1 incorrect
libc++     yes            yes                  d, dx1 incorrect
libstdc++  no             no                   d, dx1 correct
libstdc++  no             yes                  doesn't compile
libstdc++  yes            no                   d, dx1 correct
libstdc++  yes            yes                  d, dx1 correct

I'm going to give it a rest for a while, any ideas are highly appriciated!

Regards, Ed.
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