----- Original Message -----
Sent: Monday, September 12, 2005 1:48
PM
Subject: regexp /o in a sub
Wizards,
Here's one for you. I'm doing some optimizing on a
script (using timethese and cmpthese calls in stub programs) and I was
wondering about this. I know the compile-once option on regular expressions
has been maligned, but I've found that it gets me about a 3% increase on one
piece of code that uses a for loop with regexps as a pseudo-switch statement
(just like in the Camel book). Here's what I'm working on (somewhat
abbreviated):
sub
Translate
{
my ($row, $val) = @_;
my $out = "";
for ($row)
{
/^(5|6|23|24|25|26|39|40|41|45|46|51|52|53|54|55|56|60|61|63|69|70|71|72|74|76)$/o
&& do
{
$out = $hashA( $val ) };
last;
};
/^(11|12|13|14|22|28|32|44|50|58|62|64|65|73|75|82|83|85|86|91|92|93)$/o
&& do
{
$out = $hashB{$val};
last;
};
/^(0|2|7|8|9|27|31)$/o && do
{
$out =
$val;
last;
};
/^(42|43|47|48|49|84)$/o && do
{
$out = $hashC{$val};
last;
};
# ...
/^(57)$/o
&& do
{
$out = $hashP{$val};
last;
};
/^(59)$/o && do
{
$out =
$hashQ{$val};
last;
};
/^(81)$/o && do
{
$out = $hashR{$val};
last;
};
} # end for ($row)
$out = (length( $out ) > 0) ? $out :
"N/A"; # Default value for nulls
return( $row, $out );
} # sub Translate()
All the sub does is "translate" input to
output using different hashes depending on the index passed into the for
loop.
There are 18 of these "switch"
cases, running from one to 26 OR-ed possibilities in the various cases. BUT,
this code is inside a subroutine, so here's the question: does using the /o on
these regexps inside a subroutine gain anything in runtime, as opposed to
using it in mainline code? What if the script is compiled, using perlapp, into
an executable? Is there any gain with /o then (either in mainline code or in a
sub) or does any gain go out the window once the code's compiled? If it
matters, the sub will get called 94 times per run of the script.
Thanks!
I am not a guru but the algorithm appears to be
less than optinum.
Of cours if is difficult to truly judge it since
the overall schme is not described
To me you seem to say that you to:
use $row to determine which hash to use to
obtain the value from thst hash using the passed $value as
a key
1. you are trying to do 2 thing at one
time.
Perhaps you should
consider creating an array of hashes rather the a set of hashes
Now if the $row matches
none of the values in your regex ... 99 then you will loop
through 99 times rather than exiting after one
pass
Now my approach would be to do it in 2
steps.
Use hash where
the rows are the keys
and values are the indexes of the AoH
1 a one-liner can be written to
to obtain an index into the AoH
2. a one-liner can be written to use
the index and the $value (really a key) to obtain
your $out
Occam's Razor says that probably this is the
better solotion
Use the KISS principle Keep It
Simple, I am Stupid
Deane
P.S.: Yes, I *do* have way too much time on my hands.... Why else would
I be going after such niggling improvements?
;->
