Sebastian Huber <sebastian.huber@embedded-brains.de> writes:

> Our failing test is pretty basic, it just checks if fma() and fmaf() 
> library functions are present as per C99. The glibc offers also a simple 
> default implementation, for example:
>
> https://sourceware.org/git/?p=glibc.git;a=blob;f=math/s_fma.c;h=4d73af4f65d511594b2395d032a135721c578484;hb=HEAD

That implementation violates the spec though because it does two
binary operations involving two roundings, so you get a different answer
than you would with a true fma.

Is it better to implement the function incorrectly or better to not
implement it at all? If your hardware doesn't support the operation,
then doing this in software would be a lot slower than adapting your
algorithm to deal with a sequence of binary operations, even though you
will likely need more of them to reach the same accuracy.

-- 
-keith