libm reentrancy

[Gregory Pietsch]

Oh yeah, forgot about errno. I guess the best way to avoid that is to 
make sure the number you are taking the square root of isn't negative. 
-- Gregory

On 1/9/2013 4:37 AM, Marcus Hult wrote:
> Hello,
>
> Thanks for your reply Gregory.
>
> The sqrt function for instance, may set the errno variable according
> to the manual. ShouldnÂ’t this function then have a reentrant version?
> Or do I always need to use the _impure_ptr when using libm, to be thread safe?
>
> /Marcus
>
> On Tue, Jan 8, 2013 at 2:45 PM, Gregory Pietsch <gpietsch@comcast.net> wrote:
>> On 1/8/2013 6:36 AM, Marcus Hult wrote:
>>> Hello,
>>>
>>> I am a bit confused about reentrancy in the newlib libm. I have read
>>> the explanation about the _REENT_ONLY flag here:
>>> http://www.sourceware.org/ml/newlib/2003/msg00697.html.
>>>
>>> Most functions in libm does not have an _r version, but when defining
>>> the symbol _REENT_ONLY, a lot of those functions are ifndef'ed out.
>>> Why are there no reentrant versions of these functions? And how is the
>>> _REENT_ONLY flag supposed to be used with libm?
>>>
>>> To make these functions in libm thread safe, i guess i need a _reent
>>> struct in each thread and set the _impure_ptr to this when switching
>>> tasks? Or how can i assure the libm function calls are thread safe?
>>>
>>> Thanks in advance
>>>
>> Most of the libm functions do not need to change any external state, so they
>> should be thread-safe. The only ones I can think of that would be affected
>> would be the functions in fenv.h because they rely on two external states.
>> Any other comments?
>>
>> Gregory