#!/usr/bin/env perl
use warnings;
use strict;
use List::Util qw/max/;
use Benchmark qw/cmpthese/;
use constant WITHTEST => 0;

my $cols = 32;
my $row = join "\t", map { sprintf("%02d",$_) x 16 } 0..($cols-1);
my $data = ( $row . "\n" ) x 100;
open my $fh, '<', \$data or die $!;

my @wanted = (2,3,12..18,25..28,31);
#my @wanted = (2,3,10..15);
my $wanted_max = max @wanted;
my @wanted2 = (0) x $cols;
@wanted2[@wanted] = (1) x @wanted;
my ($wanted_re) = map { qr/\A$_\n?\z/ } join '\t',
	map { $_?'([^\t\n]++)':'[^\t\n]++' } @wanted2;
my $expect = join "\t", map { sprintf("%02d",$_) x 16 } @wanted;

cmpthese(-2, {
	split => sub {
		seek $fh, 0, 0 or die;
		while (<$fh>) {
			chomp;
			my @sel = (split /\t/, $_, $cols)[@wanted];
			if (WITHTEST) { die "@sel\n$expect\n"
				unless join("\t",@sel) eq $expect }
		}
	},
	scan => sub {
		seek $fh, 0, 0 or die;
		while (<$fh>) {
			chomp;
			my ($pos,$i,$prevpos,@sel)=(0,0);
			while ( $pos>=0 && $i<=$wanted_max ) {
				$prevpos = $pos;
				$pos = index($_, "\t", $pos+1);
				push @sel, substr($_, $prevpos+1,
					($pos<0 ? length : $pos)-$prevpos-1 )
						if $wanted2[$i++];
			}
			if (WITHTEST) { die "@sel\n$expect\n"
				unless join("\t",@sel) eq $expect }
		}
	},
	regex => sub {
		seek $fh, 0, 0 or die;
		while (<$fh>) {
			my @sel = /$wanted_re/ or die $_;
			if (WITHTEST) { die "@sel\n$expect\n"
				unless join("\t",@sel) eq $expect }
		}
	},
	fh => sub {
		seek $fh, 0, 0 or die;
		while ( my $line = <$fh> ) {
			chomp($line);
			open my $fh2, '<', \$line or die $!;
			local $/ = "\t";
			my @sel;
			for my $i (0..$wanted_max) {
				my $d = <$fh2>;
				next unless $wanted2[$i];
				chomp $d;
				push @sel, $d;
			}
			close $fh2;
			if (WITHTEST) { die "@sel\n$expect\n"
				unless join("\t",@sel) eq $expect }
		}
	},
});

__END__

        Rate regex    fh  scan split
regex 1456/s    --  -11%  -13%  -68%
fh    1643/s   13%    --   -1%  -64%
scan  1665/s   14%    1%    --  -64%
split 4586/s  215%  179%  175%    --