LIBM INACCURACIES

```
Description: "..if you are writing something like robot control or
inertial navigation system for aircraft, I have found
that using the toolchain libmath is only safe option.
I ported some code for converting quaternions to Euler
angles to NuttX for my project and only got it working
after switching to newlib math library.

"NuttX does not fully implement IEC 60559 floating point
from C99 (sections marked [MX] in OpenGroup specs) so if
your code assumes that some function, say pow(), actually
behaves right for all the twenty or so odd corner cases
that the standards committees have recently specified,
you might get surprises. I'd expect pow(0.0, 1.0) to
return 0.0 (as zero raised to any positive power is
well-defined in mathematics) but I get +Inf.

"NuttX atan2(-0.0, -1.0) returns +M_PI instead of correct
-M_PI. If we expect [MX] functionality, then atan2(Inf, Inf)
should return M_PI/4, instead NuttX gives NaN.

"asin(2.0) does not set domain error or return NaN. In fact
it does not return at all as the loop in it does not
converge, hanging your app.

"There are likely many other issues like these as the Rhombus
OS code has not been tested or used that much. Sorry for not
providing patches, but we found it easier just to switch the
math library."

UPDATE: 2015-09-01: A fix for the noted problems with asin()
has been applied.
2016-07-30: Numerous fixes and performance improvements from
David Alessio.

Status: Open
Priority: Low for casual users but clearly high if you need care about
these incorrect corner case behaviors in the math libraries.
```