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I don't think this is the complete answer as
read $IN1, my $buffer, -s $IN1; ++$counts{$_} for split( /^/m, $buffer );
is faster than the for.
          Rate   for  read while
for   362612/s    --   -7%  -19%
read  389496/s    7%    --  -13%
while 449755/s   24%   15%    --

        Rate   for  read while
for   4.73/s    --  -17%  -37%
read  5.73/s   21%    --  -24%
while 7.55/s   60%   32%    --

         Rate   for while  read
for   14434/s    --  -17%  -21%
while 17297/s   20%    --   -6%
read  18355/s   27%    6%    --
#!/usr/bin/perl use strict; use Benchmark qw( cmpthese ); foreach my $file qw ( /dev/null /usr/share/dict/words /etc/passwd ) { open my $IN1, '<', $file or die "could not open $file"; my @list = <$IN1>; seek( $IN1, 0, 0 ); print "$file\n"; cmpthese( -5, { for => sub { seek( $IN1, 0, 0 ); my %counts = (); ++$counts{$_} for <$IN1>; die unless keys %counts == @list; }, while => sub { seek( $IN1, 0, 0 ); my %counts = (); ++$counts{$_} while <$IN1>; die unless keys %counts == @list; }, read => sub { seek( $IN1, 0, 0 ); my %counts = (); read $IN1, my $buffer, -s $IN1; ++$counts{$_} for split( /^/m, $buffer ); die unless keys %counts == @list; }, } ); }
-- gam3
A picture is worth a thousand words, but takes 200K.

In reply to Re^2: Why is "for" much slower than "while"? by gam3
in thread Why is "for" much slower than "while"? by di

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