my @targ_shift = (
	[ \$a,  0 ],
	[ \$a,  8 ],
	[ \$a, 16 ],
	[ \$a, 24 ],
	[ \$b,  0 ],
	[ \$b,  8 ],
	[ \$b, 16 ],
	[ \$b, 24 ],
	[ \$c,  8 ],
	[ \$c, 16 ],
	[ \$c, 24 ],
);

for my $idx (0 .. $len-1) {
	my ($targ, $shift) = @{$targ_shift[$idx]};
	$$targ += $k[$idx] << $shift;
}