On Sat, 22 Jan 2005 13:34:54 -0800, John W. Krahn <[EMAIL PROTECTED]> wrote:
>
> Yes, two ways that I can think of:
>
> if ( substr( $_, 30, 3 ) =~ /\|[BNPG]\|/ ) {
>
> if ( /^.{30}\|[BNPG]\|/ ) {
>
> John
> --
For the sake of comparison, here is a set of benckmarks for a couple
of different variations on the theme, including regexing the entire
line for the pattern, regexing the pattern at a known location, and
some substring and substring/regex combos. for the heck of it, I also
tried just looking for one character, rather than a class:
CODE:
#!/usr/bin/perl
use strict ;
use warnings ;
use Benchmark ;
my $string = '| B B B B |13145551212 B B B B |N| B B B B B
B | B 0|001001|001001| 100|10|B|A|' ;
print "\n\nMultiple targets:\n\n" ;
timethese(1000000,{
'substr_regex_1' => sub { if ( substr( $string, 39, 1 ) =~
/[BNPG]/ ) { my $a = $_ } } ,
'substr_regex_3' => sub { if ( substr( $string, 38, 3 ) =~
/\|[BNPG]\|/ ) { my $a = $_ } } ,
'plain_substr' => sub { my $sub = substr( $string, 39, 1 ); if
($sub eq "B" || $sub eq "N" || $sub eq "P" || $sub eq "G") { my $a =
$sub } } ,
'plain_regex' => sub { if ( $string =~ /^.{38}\|[BNPG]\|/ ) {
my $a = $_ } },
'regex_line' => sub { if ( $string =~ /\|[BNPG]\|/ ) { my $a = $_ } }
}) ;
print "\n\nSingle target:\n\n" ;
timethese(1000000,{
'substr_regex_1' => sub { if ( substr( $string, 39, 1 ) =~ /N/ ) {
my $a = $_ } } ,
'substr_regex_3' => sub { if ( substr( $string, 38, 3 ) =~ /\|N\|/
) { my $a = $_ } } ,
'plain_substr' => sub { if ( substr( $string, 39, 1 ) eq "N" ) {
my $a = $_ } } ,
'plain_regex' => sub { if ( $string =~ /^.{38}\|N\|/ ) { my $a = $_ } },
'regex_line' => sub { if ( $string =~ /\|N\|/ ) { my $a = $_ } }
}) ;
RESULTS (representative):
Multiple targets:
Benchmark: timing 1000000 iterations of plain_regex, plain_substr,
regex_line, substr_regex_1, substr_regex_3...
plain_regex: 2 wallclock secs ( 2.69 usr + 0.03 sys = 2.72 CPU) @
367647.06/s (n=1000000)
plain_substr: 3 wallclock secs ( 3.16 usr + 0.02 sys = 3.18 CPU) @
314465.41/s (n=1000000)
regex_line: 3 wallclock secs ( 3.32 usr + 0.00 sys = 3.32 CPU) @
301204.82/s (n=1000000)
substr_regex_1: 3 wallclock secs ( 2.30 usr + 0.05 sys = 2.35 CPU)
@ 425531.91/s (n=1000000)
substr_regex_3: 3 wallclock secs ( 2.81 usr + 0.07 sys = 2.88 CPU)
@ 347222.22/s (n=1000000)
Single target:
Benchmark: timing 1000000 iterations of plain_regex, plain_substr,
regex_line, substr_regex_1, substr_regex_3...
plain_regex: 6 wallclock secs ( 3.02 usr + 0.04 sys = 3.06 CPU) @
326797.39/s (n=1000000)
plain_substr: 3 wallclock secs ( 1.78 usr + 0.02 sys = 1.80 CPU) @
555555.56/s (n=1000000)
regex_line: 1 wallclock secs ( 1.54 usr + 0.03 sys = 1.57 CPU) @
636942.68/s (n=1000000)
substr_regex_1: 2 wallclock secs ( 2.20 usr + 0.02 sys = 2.22 CPU)
@ 450450.45/s (n=1000000)
substr_regex_3: 3 wallclock secs ( 2.19 usr + 0.00 sys = 2.19 CPU)
@ 456621.00/s (n=1000000)
What was interesting to me was that although, predictably, the
substring/regex combo was consistently the best performer for the
original match, regexing the whole line was consistently the best
performer when looking for "|N|". This seems to fly in the face of
the conventional wisdom that substr is faster than m// when you know
what you're looking for and where you're looking for it.
--jay
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