Parsing null terminated strings in a binary.

[Raimo Niskanen]

Sorry, I am also to lazy to measure.

It is probably so that yours

> z_split(B, N) ->
>      case B of
> 	<<B1:N/binary,0,B2/binary>> -> {B1, B2};
> 	<<_:N/binary>> -> B;
> 	_ -> z_split(B, N+1)
>      end.

is faster than mine

> z_split(B, N) when is_binary(B), is_integer(N) ->
>      case B of
> 	<<B1:N/binary,0,B2/binary>> ->
>             {B1,B2};
>         _ when size(B) > N
>             z_split(B, N+1);
>         _ ->
>             B
>      end.

since the second clause in the first variant is done in a binary
pattern matching context, and there is a setup cost, so the
second clause may be very cheap; at least probably cheaper than 
calling size/1 (after the binary pattern matching).

It might even be so cheap that moving the size(B) call outside
the loop in variant 2 does not give any measurable improvement 
over variant 1. You will have to compare Size with N in the loop 
in that case. And for hardcore optimization the is_binary(B) and 
is_integer(N) should be moved outside the loop, of course.

So, allright, your suggested variant may be the winner!

Messen ist vissen. (Werner von Siemens) # To measure is to know.


mats.cronqvist@REDACTED (Mats Cronqvist) writes:

>    sorry to keep harping on this...
>    ...but would it be (noticably) faster to move the call to size/1 outside the loop?
>    or equivalently, how fast is size/1 (compared to the binary match)?
>    i would guess plenty fast but i'm too lazy to try it.
> 
>    mats
> 
> Raimo Niskanen wrote:
> > You are missing nothing. The code just evolved in my head to
> > what it became - some cruft was left. This might be even clearer
> > (untested):
> > z_split(B, N) when is_binary(B), is_integer(N) ->
> >      case B of
> > 	<<B1:N/binary,0,B2/binary>> ->
> >             {B1,B2};
> >         _ when size(B) > N
> >             z_split(B, N+1);
> >         _ ->
> >             B
> >      end.
> >

-- 

/ Raimo Niskanen, Erlang/OTP, Ericsson AB