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Re: libm reentrancy


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


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