[PATCH v2 3/9] math: Simplify hypotf implementation

[Wilco Dijkstra <Wilco.Dijkstra@arm.com>]

Hi Adhemerval,

+  if ((isinf (x) || isinf (y))
+      && !issignaling (x) && !issignaling (y))
+    return INFINITY;
+  if (isnan (x) || isnan (y))
+    return x + y;

These checks are inefficient. It's partly because GCC uses FP comparisons for
isinf/isnan when integer arithmetic is faster on almost all targets and more
correct for signaling NaNs. However GCC doesn't seem to treat these as
unlikely and so there are 3 comparisons and 3 taken branches before entering
the main code. If you change it to:

if (!isfinite (x) || !isfinite (y))
{
  if ((isinf (x) || isinf (y))
      && !issignaling (x) && !issignaling (y))
    return INFINITY;
 return x + y;
}

then it uses only 2 comparisons and we fallthrough into the common case.
This gives a speedup of 10%.

Wilco