[Caml-list] What is the fastest? Pattern matching or if then else

[Caml-list] What is the fastest? Pattern matching or if then else

[Francois Berenger]

Hello,

I always wondered what is the fastest (at least for integers):

match n with
   0 -> (* do something *)
| _ -> (* do something else *)

or

if n = 0 then
   (* do something *)
else
   (* do something else *)

Sometimes I have some code that would be more beautiful
if I was using only pattern matching rather than
pattern matching interspersed with if then else directives.

Is one significantly faster than the other?

Is it the same cost at runtime?

Thanks a lot,
F.

Re: [Caml-list] What is the fastest? Pattern matching or if then else

[Jacques Garrigue]

On 2012/12/07, at 11:33, Francois Berenger <berenger@riken.jp> wrote:

> Hello,
> 
> I always wondered what is the fastest (at least for integers):
> 
> match n with
>  0 -> (* do something *)
> | _ -> (* do something else *)
> 
> or
> 
> if n = 0 then
>  (* do something *)
> else
>  (* do something else *)
> 
> Sometimes I have some code that would be more beautiful
> if I was using only pattern matching rather than
> pattern matching interspersed with if then else directives.
> 
> Is one significantly faster than the other?
> 
> Is it the same cost at runtime?

$ ocaml -dlambda
        OCaml version 4.00.1

# fun n -> match n with 0 -> "this" | _ -> "that";;
(function n/1016 (if (!= n/1016 0) "that" "this"))
- : int -> string = <fun>
# fun n -> if n then "this" else "that";;
(function n/1017 (if n/1017 "this" "that"))
- : bool -> string = <fun>

In most cases, the two are going to be exactly equivalent.
Here there is a slight difference because of the handling of the constant 0.
But I would expect that to be optimized out in the native code compiler.
So the short answer is: do not let your sense of beauty be disturbed by that.

	Jacques

Re: [Caml-list] What is the fastest? Pattern matching or if then else

[Christos KK Loverdos]

On Dec 7, 2012, at 4:45 AM, Jacques Garrigue <garrigue@math.nagoya-u.ac.jp> wrote:

> On 2012/12/07, at 11:33, Francois Berenger <berenger@riken.jp> wrote:
> 
>> Hello,
>> 
>> I always wondered what is the fastest (at least for integers):
>> 
>> match n with
>> 0 -> (* do something *)
>> | _ -> (* do something else *)
>> 
>> or
>> 
>> if n = 0 then
>> (* do something *)
>> else
>> (* do something else *)
>> 
>> Sometimes I have some code that would be more beautiful
>> if I was using only pattern matching rather than
>> pattern matching interspersed with if then else directives.
>> 
>> Is one significantly faster than the other?
>> 
>> Is it the same cost at runtime?
> 
> $ ocaml -dlambda
>        OCaml version 4.00.1
> 
> # fun n -> match n with 0 -> "this" | _ -> "that";;
> (function n/1016 (if (!= n/1016 0) "that" "this"))
> - : int -> string = <fun>
> # fun n -> if n then "this" else "that";;
> (function n/1017 (if n/1017 "this" "that"))
> - : bool -> string = <fun>
> 
> In most cases, the two are going to be exactly equivalent.
> Here there is a slight difference because of the handling of the constant 0.
> But I would expect that to be optimized out in the native code compiler.
> So the short answer is:

> do not let your sense of beauty be disturbed by that.

+1

> 
> 	Jacques
> 
> 
> -- 
> Caml-list mailing list.  Subscription management and archives:
> https://sympa.inria.fr/sympa/arc/caml-list
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--
Christos KK Loverdos
@loverdos
stepsinscala.com

Everything that is really great and inspiring is created by the individual who can labor in freedom — Albert Einstein

Re: [Caml-list] What is the fastest? Pattern matching or if then else

[Francois Berenger]

On 12/07/2012 05:06 PM, Christophe TROESTLER wrote:
> On Fri, 7 Dec 2012 11:33:52 +0900, Francois Berenger wrote:
>>
>> Hello,
>>
>> I always wondered what is the fastest (at least for integers):
>
> In general, you can check these things yourself:
> https://github.com/Chris00/ocaml-benchmark

Christophe TROESTLER even did an OPAM package for benchmark:

opam update
opam install benchmark

Thanks!
F.

Re: [Caml-list] What is the fastest? Pattern matching or if then else

[Francois Berenger]

On 12/10/2012 09:27 AM, Christophe TROESTLER wrote:
> On Mon, 10 Dec 2012 09:06:14 +0900, Francois Berenger wrote:
>>
>> On 12/07/2012 05:06 PM, Christophe TROESTLER wrote:
>>> On Fri, 7 Dec 2012 11:33:52 +0900, Francois Berenger wrote:
>>>>
>>>> Hello,
>>>>
>>>> I always wondered what is the fastest (at least for integers):
>>>
>>> In general, you can check these things yourself:
>>> https://github.com/Chris00/ocaml-benchmark
>>
>> Christophe TROESTLER even did an OPAM package for benchmark:
>>
>> opam update
>> opam install benchmark
>>
>> Thanks!
>
> Well, I have not done it, it seems we should rather thank Anil!

Sorry!