[PATCH v4 13/21] math: Remove the SVID error handling from atan2f

[Wilco Dijkstra]

Hi Adhemerval,

-  return asdouble (t);
+  double r = asdouble (t);
+  float rf = r;
+  if (__glibc_unlikely (fabsf (rf) < 0x1p-126f))
+    __set_errno (ERANGE);
+  return rf;
 }

We should only set errno on underflow to zero - it's more efficient to
test for zero 'rf' as well.

Also, it's better to use __math_uflowf rather than explicitly setting errno.
This shows we're dealing with underflow but also allows us to build with
errno turned off.

Cheers,
Wilco