Minor performance improments
Mostly useful as lesson learned.
1) The double precision constant forces the compiler to convert
the single precision variable to double, then do the multiplication
in double and then convert back. Using the single precsion
constant in double reduces the accuracy (the calculation is still done
double but the constant has only single precision).
2) Using a temporary array instead of a temporary scalar causes ICC14 to
generate an extra store.
Change-Id: Ib320ac2ae4ff80ce48277544abff468c483cc83a