bstring.erl in the next release?

Sean Hinde <>
Fri Sep 21 12:54:58 CEST 2001


Hi,

>  (=?iso-8859-1?q?J=E9r=F4me?= Marant) writes:
> >
> >Hi,
> >
> >  I was seeking for a binary implementation of string functions
> >  and someone gracefully pointed me to the mail archive at
> > 
> >  
> http://www.erlang.org/ml-archive/erlang-> questions/200103/msg00134.html
> >
> >  What about integrating this module in the next Erlang 
> release? (unless
> >  it is already there).
> 
> However, as the string library is mainly about pulling apart strings
> then a bstring library would probably be in place.  A bregexp as well
> would be nice.
> 
> Sean, have you tested the efficiency of your drivers against using
> bit-syntax directly?

Yes, I did some quick tests.

Some quick and dirty results (figures given are averages over quite a number
of runs):

L = lists:seq(1,255).
B = list_to_binary(L).

1> timer:tc(string, chr, [L, 255]).
{76, 255}
2> timer:tc(bstring, chr, [B, 255]). % Driver
{40, 255}
3> timer:tc(bstring, chr2, [B, 255]). % Bitsyntax linear search
{260, 255}

The current bitsyntax doesn't appear to do that well if parsing byte by
byte. 

We have found it to be much quicker than list crunching for our protocol
decode functions though. e.g Splitting 100 octets into 10 groups of 10
octets is much quicker with bitsyntax than parsing every byte through a
list.

bifs for bstring:chr, str, rchr, rstr, and perhaps reverse would be one way
to redress the balance.

Some addition to the bitsyntax a la the original would be even better:

1> <<_:Pos/binary, 4, Tail/binary>> = <<1,1,1,1,1,1,1,1,1,4>>.
<<1,1,1,1,1,1,1,1,1,4>>
2> Pos.
10

Rgds,
Sean



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