Re: [Caml-list] Re: float boxing (was: matrix-matrix multiply)

[malc <malc@pulsesoft.com>]

On Wed, 23 Oct 2002, Christophe TROESTLER wrote:

> On Sun, 20 Oct 2002, Issac Trotts <ijtrotts@ucdavis.edu> wrote:
> > 
> > You might try converting your references to mutable fields.
> >
> > let x = ref 1.0 in
> > let n = int_of_string Sys.argv.(1) in
> > for i = 1 to n do x := !x +. 1.0 done
> > 
> > ./ref 100000000  2.51s user 0.00s system 99% cpu 2.515 total
> > 
> > type t = { mutable f:float };;
> > let x = { f = 1.0 } in
> > let n = int_of_string Sys.argv.(1) in
> > for i = 1 to n do x.f <- x.f +. 1.0 done
> >
> > ./ref2 100000000  1.54s user 0.01s system 100% cpu 1.542 total
> 
> A few questions in view of this.  First, on my machine (AMD Athlon
> 1GHz running GNU/Linux), the timings give a preference to ref.ml
> 
> time ./ref 100000000
> real    0m1.279s user    0m1.280s sys     0m0.000s
> time ./ref2 100000000
> real    0m1.411s user    0m1.380s sys     0m0.000s
> 
> What could be a reason for that?

I think the reason is simple, both are more or less nop operations,
x or x.f is not used anywhere, hence no need to allocate the float.
This short example highlights the difference:

let useref n = 
  let x = ref 1.0 in
  for i = 1 to n do x := !x +. 1.0 done;
  !x

type t = { mutable f:float };;
let userec n = 
  let x = { f = 1.0 } in
  for i = 1 to n do x.f <- x.f +. 1.0 done;
  x.f

let _ =
  let n = int_of_string Sys.argv.(2) in
  Printf.printf "%f\n"
  (if Sys.argv.(1) = "ref" then
    useref n
  else
    userec n)

ref# time ./refrec rec 100000000
100000001.000000

real    0m2.283s
user    0m2.280s
sys     0m0.000s
ref# time ./refrec ref 100000000
100000001.000000

real    0m1.916s
user    0m1.910s
sys     0m0.010s

More or less same machine here.

-- 
mailto:malc@pulsesoft.com

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