my $aref = $matches{ $fasta_id }{ $sitekey };
my( $lo, $hi ) = ( 0, scalar @{ $aref } );
++$lo while ($aref->[ $lo + 1 ] < $lowerlimit && $lo < $hi-2);
 --$hi while ($aref->[ $hi - 1 ] > $upperlimit && $hi > 0  );

##</code><code>##

@a = ( 1 .. 100 );
$val = 43.56;
$nearby = zoom($val,@a);
# $nearby now is essentially an index for @a somewhere in the near
# vicinity of 43.56, say 40 or so..