- my $unit = int(log(abs $_[0] || 1) / log(10) - 3*($_[0] < 1) + 1e-15);
- my $float = $_[0] !~ /^0*[-0-9]{1,3}$/;
- 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]
+ my $unit = (
+ log(abs $_[0] || 1) / log(10)
+ - 3 * (abs($_[0]) < .9995) # shift to smaller unit if below 1
+ + 1e-15 # float imprecision
+ );
+ my $decimal = ($unit % 3) == ($unit < 0);
+ $unit -= log($decimal ? .995 : .9995) / log(10); # rounded
+ $decimal = ($unit % 3) == ($unit < 0);
+ $decimal &&= $_[0] !~ /^-?0*[0-9]{1,3}$/; # integer 0..999
+ sprintf('%*.*f%1s',
+ 3 + ($_[0] < 0), # digits plus optional negative sign
+ $decimal, # tenths
+ $_[0] / 1000 ** int($unit/3), # number
+ $#{$opt{units}} * 1.5 < abs $unit ? sprintf('e%d', $unit) :
+ $opt{units}->[$unit/3] # suffix