Re^4: better (faster) way of writing regexp

[Marshall]

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%     --

[ikegami]

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%     --

(Threaded 32-bit build on linux)

Interesting.

[Marshall]

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

[ikegami]

I "win"! :) My machine, not the one I ran the benchmark on:

Number of cores         1 (max 1)
Number of threads       1 (max 1)
Name                    Intel Pentium 4
Codename                Northwood
Specification           Intel(R) Pentium(R) 4 CPU 2.66GHz
Package (platform ID)   Socket 478 mPGA (0x2)
CPUID                   F.2.7
Extended CPUID          F.2
Brand ID                9
Core Stepping           C1
Technology              0.13 um
Core Speed              2004.5 MHz
Multiplier x FSB        20.0 x 100.2 MHz
Rated Bus speed         400.9 MHz
Stock frequency         2666 MHz
Instructions sets       MMX, SSE, SSE2
L1 Data cache           8 KBytes, 4-way set associative, 64-byte line 
+size
Trace cache             12 Kuops, 8-way set associative
L2 cache                512 KBytes, 8-way set associative, 64-byte lin
+e size
FID/VID Control         no

From that machine:

This is Perl 5.010001
           Rate  range repeat  isook unpack substr
range  117311/s     --    -6%    -7%   -24%   -81%
repeat 124414/s     6%     --    -2%   -20%   -80%
isook  126456/s     8%     2%     --   -18%   -79%
unpack 155069/s    32%    25%    23%     --   -74%
substr 607361/s   418%   388%   380%   292%     --

I'm scared of looking at the stats of my tv computer (aka Frankenputer). It's some kind of P3, for starters.