Re^3: better (faster) way of writing regexp

I'm not sure why you have the regex engine check if each character is not a newline in isook. Use the "s" modifier!

Interesting about pack. I heard the overhead to start the regex engine went up in 5.10, but it seems rather minor when put into perspective. ...except I can't replicate your results.

use strict;
use warnings;

use Benchmark qw(:all);

print("This is Perl $]\n");

my %tests = (
    repeat => 'my ($y,$m,$d) = $date =~ /(\\d\\d\\d\\d)(\\d\\d)(\\d\\d
+)/;',
    range  => 'my ($y,$m,$d) = $date =~ /(\\d{4})(\\d{2})(\\d{2})/;',
    isook  => 'my ($y,$m,$d) = $date =~ /(....)(..)(..)/s;',
    unpack => 'my ($y,$m,$d) = unpack "A4 A2 A2", $date;',
);

# These don't result in any opcodes.
$_ = 'use strict; use warnings; our $date; '.$_
    for values(%tests);

our $date = '20091202';

my $results = cmpthese(-3, \%tests);
[download]

This is Perl 5.010000
           Rate  range repeat  isook unpack
range  405773/s     --    -6%    -8%   -46%
repeat 432956/s     7%     --    -2%   -43%
isook  441233/s     9%     2%     --   -42%
unpack 757010/s    87%    75%    72%     --

This is Perl 5.010000
           Rate  range  isook repeat unpack
range  398141/s     --    -7%    -7%   -47%
isook  427913/s     7%     --    -0%   -43%
repeat 429311/s     8%     0%     --   -43%
unpack 751802/s    89%    76%    75%     --

This is Perl 5.010000
           Rate  range repeat  isook unpack
range  415595/s     --    -7%    -8%   -45%
repeat 445365/s     7%     --    -1%   -41%
isook  449974/s     8%     1%     --   -40%
unpack 754290/s    81%    69%    68%     --
[download]

The faster way seems to be using the capture made of dots as in "isook"

You haven't shown that. Any difference less than 5% should be ignored. It's within the error margin.

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Re^4: better (faster) way of writing regexp by JavaFan (Canon) on Dec 02, 2009 at 18:19 UTC
`# These don't result in any opcodes. $_ = "use strict; use warnings; our $date; $_" for values(%tests);` [download] Indeed no opcodes, as it doesn't compile. You're interpolating a variable that hasn't been introduced to perl yet.	[reply] [d/l]
Re^5: better (faster) way of writing regexp by ikegami (Patriarch) on Dec 02, 2009 at 18:33 UTC
~~It doesn't later either. In other words, they're not executed during Benchmarking.~~ Ah, I misread earlier. I had posted the wrong copy of the code. Fixed.	[reply]
Re^4: better (faster) way of writing regexp by Marshall (Canon) on Dec 03, 2009 at 07:52 UTC
Ikegami, I am curious if you can replicate my results with the substr idea plugged into your benchmark code? Update: the reason I ask is that I know you have a very fast 64 bit machine and there could be some differences between my much slower, older 32 bit machine. use strict; use warnings; use Benchmark qw(:all); print("This is Perl $]\n"); my %tests = ( repeat => 'my ($y,$m,$d) = $date =~ /(\\d\\d\\d\\d)(\\d\\d)(\\d\\d +)/;', range => 'my ($y,$m,$d) = $date =~ /(\\d{4})(\\d{2})(\\d{2})/;', isook => 'my ($y,$m,$d) = $date =~ /(....)(..)(..)/s;', unpack => 'my ($y,$m,$d) = unpack "A4 A2 A2", $date;', substr => 'my $y = substr($date,0,4);my $m = substr($date,4,2);my +$d = substr($date,6,2);' ); # These don't result in any opcodes. $_ = 'use strict; use warnings; our $date; '.$_ for values(%tests); our $date = '20091202'; my $results = cmpthese(-3, \%tests); __END__ This is Perl 5.010000 Rate range isook repeat unpack substr range 151695/s -- -7% -8% -54% -85% isook 162964/s 7% -- -1% -50% -84% repeat 165314/s 9% 1% -- -49% -84% unpack 326977/s 116% 101% 98% -- -68% substr 1010101/s 566% 520% 511% 209% -- [download]	[reply] [d/l]
Re^5: better (faster) way of writing regexp by ikegami (Patriarch) on Dec 03, 2009 at 17:42 UTC
I know you have a very fast 64 bit machine Dream on! My 32-bit machine doesn't even have a virtual second core from hyperthreading. I'm not sure what my work machine is, but it's also 32-bit. My earlier run was on my work machine. This is on my work machine too: `This is Perl 5.010000 Rate range repeat isook unpack substr range 416206/s -- -6% -8% -45% -67% repeat 443742/s 7% -- -1% -41% -65% isook 450082/s 8% 1% -- -41% -64% unpack 756739/s 82% 71% 68% -- -40% substr 1257912/s 202% 183% 179% 66% -- This is Perl 5.010000 Rate range repeat isook unpack substr range 415726/s -- -5% -8% -47% -67% repeat 436462/s 5% -- -4% -44% -65% isook 454041/s 9% 4% -- -42% -64% unpack 779486/s 88% 79% 72% -- -38% substr 1262559/s 204% 189% 178% 62% --` [download] (Threaded 32-bit build on linux) Interesting.	[reply] [d/l]
Re^6: better (faster) way of writing regexp by Marshall (Canon) on Dec 03, 2009 at 22:28 UTC
Interesting... The ratio's aren't the same as on my machine, but it appears that substr() is pretty quick on both of our machines. I don't know a Linux utility for this, but in the Windows world, CPU-Z http://www.cpuid.com/cpuz.php shows a lot of info about processors... It is hard for me to imagine that you don't have at least a multi-threaded processor given the raw speed of your machine for a single thread. If I run two "number cruncher" apps at once, the performance is not 2x, but rather like 1.4x. I have old memory technology and my machine becomes memory bound. To Windows XP Pro, my machine looks pretty much like 2 CPU's except that 1+1 != 2, only about 1.4! And of course when I do that, my computer turns into a "space heater"!. When the winter gets colder, I run some BOINC project like seti@home, etc. on the theory that I might as well be doing something at least marginally useful while I am generating heat! Anyway this is what I have:(in the scheme of things, a Prescott is a wimp) Processor 1 (ID = 0) Number of cores 1 (max 1) Number of threads 2 (max 2) Name Intel Pentium 4 Codename Prescott Specification Intel(R) Pentium(R) 4 CPU 3.00GHz Package Socket 478 mPGA (platform ID = 2h) CPUID F.4.1 Extended CPUID F.4 Core Stepping E0 Technology 90 nm Core Speed 3015.1 MHz (15.0 x 201.0 MHz) Rated Bus speed 804.0 MHz Stock frequency 3000 MHz Instructions sets MMX, SSE, SSE2, SSE3 L1 Data cache 16 KBytes, 8-way set associative, 64-byte line si +ze Trace cache 12 Kuops, 8-way set associative L2 cache 1024 KBytes, 8-way set associative, 64-byte line size FID/VID Control no [download]	[reply] [d/l]
Re^7: better (faster) way of writing regexp by ikegami (Patriarch) on Dec 03, 2009 at 22:38 UTC