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I can squeeze another 20% or so out of it actually 23% on my systems with some more micro-optimizations. The most significant change is in the inner loop, where Ive changed
substr( $q, 0, $k ) = reverse substr( $q, 0, $k );
$q = reverse(substr($q, 0, $k)) . substr($q, $k);
Here's the code:
sub fannkuch { use bytes; # This makes it fractionally faster my ( $copy, $level, $split ) = ( @_, 0, 1 ); my ( $index, $next, $length ) = ( $level, $level + 1, length( $cop +y ) ); if ($next == $length) { $index = $split - 1; substr($copy, $index, 0) = chop($copy); } my ( $q, $k ); do { if ($next == $length) { if (($k = ord($q = $copy)) != $length || $level >= $maxflips) { # Declaring $flips in here means we can reset it # with a single op (compared with the three you # need for C<$flips = 0>). my $flips; # This is a touch faster than a "proper" loop, # because it doesn't push a new context. $q = reverse(substr( $q, 0, $k )) . substr($q, $k), ++$flips while ($k=ord($q)) != 1; no warnings "uninitialized"; # $flips may be undef if ( $flips >= $maxflips ) { if ( $flips == $maxflips) { push @max_sequence, $copy; } else { ($maxflips, @max_sequence) = ($flips, $copy); } } } } else { fannkuch( $copy, $next, $split ); $split = $next if $index == $split; } substr($copy, $index-1, 2) = reverse substr($copy, $index-1, 2 +); } while $index--; $maxflips; # faster than an explicit return }

In reply to Re: Speed/Efficiency tweaks for a fannkuch benchmark script? by robin
in thread Speed/Efficiency tweaks for a fannkuch benchmark script? by thundergnat

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    [erix]: if you're interested in tsv file reading in pg, look at file_fdw
    [erix]: aka: create extension if not exists file_fdw;
    [erix]: the annoying thing is that during setup of the 'foreign table' you have to specify all the columns. But that is reasonably automatable (just reading header line, and contruct the needed CREATE FOREIGN TABLE' statement)

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