(Free42) roundoff for complex SQRT

[Paul Dale]

I hate it when I can't find a reference.

The idea is to build a correctly rounded cross product from which a two dimensional dot product and complex multiplication can be done. I seem to remember it taking three FMA operations instead of two multiplications.

FMA can also be useful for statistical accumulations and polynomial evaluations using Horner's method.

I'm sure I'll remember eventually,

Pauli