Boost logo

Boost :

From: John Moeller (fishcorn_at_[hidden])
Date: 2008-05-19 11:50:42

Hervé Brönnimann <hervebronnimann <at>> writes:

> On May 15, 2008, at 10:40 AM, John Moeller wrote:
> > Fair enough. I think, though, if you're going to try to make sure
> > that
> > the compiler doesn't miss multiplication by 1, you may as well go
> > all the
> > way and add another template parameter to capture N%2, and get rid
> > of the
> > ternary statement:
> To be clear, I'm not concerned about optimizing multiplication by 1
> for builtin types, of course. But it seems to me that the compiler
> shouldn't really be able to optimize for user-defined types (what if
> multiplication isn't inlined, for instance...)

And regardless of whether the type is builtin or not, branching with template
parameters will accomplish the same task as letting the compiler decide to
inline a ternary statement, except that it will be explicit. There is zero
chance of the compiler generating more instructions than are needed (unless
inlining breaks down). I know that this ternary statement's condition may be
evaluated at compile time, so there is little chance of more than one branch
being generated, but why not just make it explicit?

(From an aesthetic standpoint, I think branching with a template parameter
expresses the recursion very elegantly (two branches, one base condition), and
doesn't get in the way at all. Elegance isn't really what matters here,

My response wasn't motivated emotionally; I agree with your argument about UDT
multiplication (as I did when I wrote my response in the first place). I'm
just saying it would be advantageous to follow the process further.

John Moeller

Boost list run by bdawes at, gregod at, cpdaniel at, john at