Speeding up

[gamo]

I want to speed up this code:

$kk=0;
for (0..7){
$kk++ if (index($k,$res[$_]) >=0);
}
if ($kk==8){
...

TIA

 

[Brian Wakem]

I want to speed up this code:

$kk=0;
for (0..7){
$kk++ if (index($k,$res[$_]) >=0);
}
if ($kk==8){
...

TIA

You haven't told us what is in $k or @res. But in any case, index will
likely be the fastest way to do it.

Using != -1 instead of >=0 might buy you a millionth of a second.

 

[Anno Siegel]

I want to speed up this code:

$kk=0;
for (0..7){
$kk++ if (index($k,$res[$_]) >=0);
}
if ($kk==8){
...

Try (untested)

unless ( grep index( $k, $res[ $_]) < 0, 0 .. 7 ) {

Benchmark it. It is shorter, it may or may not be faster.

Anno

Anno

 

[gamo]

Try (untested)

unless ( grep index( $k, $res[ $_]) < 0, 0 .. 7 ) {

Benchmark it. It is shorter, it may or may not be faster.

Anno

#!/usr/local/bin/perl -w

use Benchmark 'cmpthese';

$k = "11-12-13-14-15-16-17-18-";
@res = qw( 11 12 13 14 15 16 17 18);


cmpthese -5, {
'for' => sub {
$kk=0;
for (0..7){
$kk++ if (index($k,$res[$_]) >=0);
}
if ($kk==8){
;
}
},
'grep' => sub {
unless ( grep index( $k, $res[ $_]) < 0, 0 .. 7 ) {
;
}
},
};

__END__



Rate for grep
for 167564/s -- -36%
grep 261988/s 56% --

Thank you for the responses. The problem was more related with $k.
Doing

for $i (){
for $j (){
for $k (reverse @combinations){
code;
}
}
}

the thing was severely improved.

Thank you for your responses.

Cheers.

 

[A. Sinan Unur]

I want to speed up this code:

$kk=0;
for (0..7){
$kk++ if (index($k,$res[$_]) >=0);
}
if ($kk==8){

Have you measured where your program actually spends it time?

Well, here are some meaningless results:

#!/usr/bin/perl

use strict;
use warnings;

my $s = <<EO_TEXT;
gamo posted a question about making a meaningless piece of code
faster. He did not provide any sample data nor did he provide a
short but complete script others can run. It looks like gamo has
not read the posting guidelines. Please do.
EO_TEXT

my @r = qw( gamo post question provide FAQ short incomplete don't);

sub gamo_index {
my $kk = 0;
for (0 .. 7) {
$kk++ if 0 <= index $s, $r[$_];
}
}

sub gamo_grep { scalar grep { 0 <= index $s, $_ } @r }

use Benchmark qw( cmpthese );

cmpthese -1, {
gamo_index => \&gamo_index,
gamo_grep => \&gamo_grep,
};

__END__

D:\Home\asu1\UseNet\clpmisc\faster> f
Rate gamo_index gamo_grep
gamo_index 57389/s -- -34%
gamo_grep 86624/s 51% --

However, a meaningful optimization would look at the overall problem you
are trying to solve. Trying to make individual lines go faster is
generally meaningless.

Sinan

 

[gamo]

gamo ([email protected]) wrote on MMMMDLV September MCMXCIII in September?
....
The obvious improvement is to stop testing as soon as one test
fails, as you only want to do something if all cases match.
You'd have to benchmark with data that's relevant for your application
(and test both data that matches *and* data that fails).

Ok, but I can't test all the real problem, which ranges varies too much.

One way of writing would be:


if (index ($k => $res [0]) >= 0 &&
index ($k => $res [1]) >= 0 &&
index ($k => $res [2]) >= 0 &&
index ($k => $res [3]) >= 0 &&
index ($k => $res [4]) >= 0 &&
index ($k => $res [5]) >= 0 &&
index ($k => $res [6]) >= 0 &&
index ($k => $res [7]) >= 0) {
...
}


For engineering purposes not the best, but you lose the overhead of
a loop (and no additional scopes to enter), and gain the benefit of
skipping the rest of the tests if one fails.



Abigail

Thank you very much. We have a winner

Rate for grep if
for 163424/s -- -36% -43%
grep 254970/s 56% -- -11%
if 285632/s 75% 12% --

The problem as I said before is not yet solved.
Reversing the matrix of $k only speed up initial calculations.
Thus, it's neccesary to optimize this part of code, which is
executed millions and millions times.

Best regards

 

[Uri Guttman]

g> I want to speed up this code:

g> $kk=0;
g> for (0..7){
g> $kk++ if (index($k,$res[$_]) >=0);
g> }
g> if ($kk==8){
g> ...

my main suggestion is to loop over the @res values directly and not
index to get them. you don't seem to really need the value of $kk (and
it will never get to 8 with a 0 .. 7 loop so that is a bug!)

if you must have a check for failure you could use a flag (eww) or wrap
the test in a sub like this (untested):

sub check_for_foolish_value {

my $text = shift ;

foreach my $foolish_value ( @_ ) {

return $foolish_value if
index( $text, $foolish_value ) >= 0 ;
}

return ;
}

i bet even with the sub overhead it will be faster than all that array
indexing. but i could be wrong so someone else should benchmark it.

uri

 

[gamo]

g> I want to speed up this code:

g> $kk=0;
g> for (0..7){
g> $kk++ if (index($k,$res[$_]) >=0);
g> }
g> if ($kk==8){
g> ...

my main suggestion is to loop over the @res values directly and not

That could be fine.

index to get them. you don't seem to really need the value of $kk (and
it will never get to 8 with a 0 .. 7 loop so that is a bug!)

It is not. From 0 to 7 there are 8 evaluations.

if you must have a check for failure you could use a flag (eww) or wrap
the test in a sub like this (untested):

sub check_for_foolish_value {

my $text = shift ;

foreach my $foolish_value ( @_ ) {

return $foolish_value if
index( $text, $foolish_value ) >= 0 ;
}

return ;
}

i bet even with the sub overhead it will be faster than all that array
indexing. but i could be wrong so someone else should benchmark it.

uri

Best regards.


--
http://www.telecable.es/personales/gamo/
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perl -e 'print 111_111_111**2,"\n";'

 

[Uri Guttman]

g> $kk=0;
g> for (0..7){
g> }
g> if ($kk==8){
g> ...

g> It is not. From 0 to 7 there are 8 evaluations.


i never said the number of evaluations wasn't 8. i said $kk will never
be 8 so the if ($kk==8) will always fail. that is a bug. a classic off
by one or picket fence error. in a c style for loop, $kk would probably
become 8 so it would fail of the loop. in foreach ( $n .. $m ) loops the
loop iterator gets $m as its last value.

uri

 

[Uri Guttman]

A> for (0 .. 7) {
A> $kk ++;
A> }
A> if ($kk == 8) {
A> print "uri is wrong\n";
A> }


A> __END__
A> uri is wrong

blech, i forgot about the $kk++ in the OP's code. it's been a couple of
days since i saw it.

uri