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Re: Fastest split possible

by marioroy (Parson)
on Nov 07, 2019 at 00:29 UTC ( #11108409=note: print w/replies, xml ) Need Help??


in reply to Fastest split possible

Update: Added regex example.

Hello all :) I tried trimming the left side of the string. Plus incorporated the memfh example by davido. I'm curious too.

Split improves ~ 2x faster for this demonstration with Perl 5.22.x and later releases. That is the case on macOS.

use strict; use warnings; use Time::HiRes 'time'; my $huge_string = "aaa bbb\nccc ddd\neee fff\nggg hhh\niii jjj\nkkk ll +l\nmmm nnn\n"; # concatenate string exponentially to 917,504 lines $huge_string .= $huge_string for 1..17; # memfh { my $string = $huge_string; my $start = time; open my $memfh, '<', \$string; my @lines = <$memfh>; close $memfh; printf "duration memfh: %0.3f seconds\n", time - $start; printf "%d lines\n\n", scalar(@lines); } # regex { my $string = $huge_string; my $start = time; my @lines; while ( $string =~ /([^\n]+\n)/mg ) { my $line = $1; # save $1 to not lose the value push @lines, $line; } printf "duration regex: %0.3f seconds\n", time - $start; printf "%d lines\n\n", scalar(@lines); } # split { my $string = $huge_string; my $start = time; my @lines = split(/\n/, $string); printf "duration split: %0.3f seconds\n", time - $start; printf "%d lines\n\n", scalar(@lines); } # trim { my $string = $huge_string; my $start = time; my @lines; while ( my $line = substr($string, 0, index($string, "\n") + 1, '' +) ) { push @lines, $line; } printf "duration trim : %0.3f seconds\n", time - $start; printf "%d lines\n\n", scalar(@lines); }

Output - Perl 5.28.2

duration memfh: 0.384 seconds 917504 lines duration regex: 0.387 seconds 917504 lines duration split: 0.067 seconds 917504 lines duration trim : 0.201 seconds 917504 lines

Another machine - Perl 5.26.1

duration memfh: 0.477 seconds 917504 lines duration regex: 0.445 seconds 917504 lines duration split: 0.065 seconds 917504 lines duration trim : 0.259 seconds 917504 lines

Same machine - Perl 5.18.2

duration memfh: 0.530 seconds 917504 lines duration regex: 0.490 seconds 917504 lines duration split: 0.130 seconds 917504 lines duration trim : 0.261 seconds 917504 lines

Regards, Mario

Replies are listed 'Best First'.
Re^2: Fastest split possible
by marioroy (Parson) on Nov 08, 2019 at 03:22 UTC

    Update 1: Added walk2 by pushing to stack.
    Update 2: The string length now obtained inside C.
    Update 3: Changed from for loop to while loop.

    Ah, I tried Inline::C. Walk1 runs faster than split in older Perl <= 5.20.x.

    ... use Inline 'C' => <<'END_C'; #include <stdlib.h> #include <string.h> SV * c_walk1(SV *sv) { STRLEN len; const char *s = SvPV_const(sv, len); const char *m = s, *strend = s + len; AV *ret = newAV(); while (s < strend) { if (*s++ == '\n') { av_push(ret, newSVpvn(m, s - m)); m = s; } } return newRV_noinc((SV *) ret); } void c_walk2(SV *sv) { STRLEN len; const char *s = SvPV_const(sv, len); const char *m = s, *strend = s + len; Inline_Stack_Vars; Inline_Stack_Reset; while (s < strend) { if (*s++ == '\n') { Inline_Stack_Push(sv_2mortal(newSVpvn(m, s - m))); m = s; } } Inline_Stack_Done; } END_C # walk1 - receive array ref { my $string = $huge_string; my $start = time; my $lines = c_walk1($string); printf "duration walk1: %0.3f seconds\n", time - $start; printf "%d lines\n\n", scalar(@$lines); } # walk2 - receive list { my $string = $huge_string; my $start = time; my @lines = c_walk2($string); printf "duration walk2: %0.3f seconds\n", time - $start; printf "%d lines\n\n", scalar(@lines); }

    Output from Perl 5.20.3 and Perl 5.26.1

    $ /opt/perl-5.20.3/bin/perl demo.pl duration memfh: 0.526 seconds 917504 lines duration regex: 0.448 seconds 917504 lines duration split: 0.110 seconds 917504 lines duration trim : 0.268 seconds 917504 lines duration walk1: 0.073 seconds 917504 lines duration walk2: 0.110 seconds 917504 lines
    $ /opt/perl-5.26.1/bin/perl demo.pl duration memfh: 0.479 seconds 917504 lines duration regex: 0.442 seconds 917504 lines duration split: 0.066 seconds 917504 lines duration trim : 0.259 seconds 917504 lines duration walk1: 0.070 seconds 917504 lines duration walk2: 0.084 seconds 917504 lines

    Regards, Mario

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