libm reentrancy

[Gregory Pietsch]

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