Re: [Caml-list] Optimizing Float Ref's

[Alain Frisch <alain@frisch.fr>]

On 31/03/2010 19:21, Dmitry Bely wrote:
> On Thu, Sep 3, 2009 at 1:44 PM, Xavier Leroy<Xavier.Leroy@inria.fr>  wrote:
> (...)
>>> But, I thought that float ref's were automatically unboxed by the compiler
>>> when they didn't escape the local context.
>>
>> Yes, if all uses of the float ref are unboxed, which is the case in
>> your code.
>
> let max_val (a:float array) =
>    let m = ref min_float in
>    for i = 0 to (Array.length a) - 1 do
>      if a.(i)>  !m
>      then m := a.(i)
>    done;
>    !m
>
> !m is not unboxed (Ocaml 3.11). Should it?

As far as I can tell, the boxing for the reference cell is removed by 
the compiler (that is, the reference is implemented as a mutable local 
variable), but not the boxing for the float contained in the reference. 
Since a is a float array, it is needed to box the float before putting 
it in the reference, hence the allocation.


-- Alain