At the high level the second item looks more efficient, however if you look at the generated IL, what you will notice is that both of them basically do the same thing.
dcl_literal l0, 2.30258509299, 2.30258509299, 2.30258509299, 2.30258509299
mov r0, l0
log r1, inY
div Y r1, r0
mov o0, Y
or something similiar to this.
In essence the performance for the two cases is identical as the same number of ALU instructions need to be run.