If you know that x is never negative, the fastest method on my machine is currently
ccall(:exp, Cdouble, (Cdouble,), 1.4 * ccall(:log, Cdouble, (Cdouble,), y))
If you know that x is never negative, the fastest method on my machine is currently
ccall(:exp, Cdouble, (Cdouble,), 1.4 * ccall(:log, Cdouble, (Cdouble,), y))