+sub sival {
+ my $unit = int(log(abs $_[0] || 1) / log(10) - 3*($_[0] < 1) + 1e-15);
+ my $float = $_[0] !~ /\A0*[-0-9]{1,3}\z/;
+ return sprintf('%3.*f%1s',
+ $float && ($unit % 3) == ($unit < 0), # tenths
+ $_[0] / 1000 ** int($unit/3), # number
+ $#{$opt{units}} * 1.5 < abs $unit ? "e$unit" : $opt{units}->[$unit/3]
+ );
+}
+