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Re: libm reentrancy

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:

Thanks for your reply Gregory.

The sqrt function for instance, may set the errno variable according
to the manual. Shouldn’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?


On Tue, Jan 8, 2013 at 2:45 PM, Gregory Pietsch <> wrote:
On 1/8/2013 6:36 AM, Marcus Hult wrote:

I am a bit confused about reentrancy in the newlib libm. I have read
the explanation about the _REENT_ONLY flag here:

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?


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