I have yet to find a display format for arbitrary floating point numbers that I like much. I wanted something closer to "Engineering notation" (exponents are always a multiple of 3) but this works for now.

The code is tested but could probably be improved a great deal.

I'd like to be able to make the width a parameter (instead of fixed at 9). Being able to go as low as 7 (or even 6) would be way cool. 

#!/usr/bin/perl -w
use strict;

Main();
exit( 0 );

{

    my( %fmt4exp, @exps2fmt, $fullfmt );

    BEGIN {
        %fmt4exp= (
            -100 => '+1.0e-999',
             -10 => '+1.00e-99',
              -5 => '+1.000e-9',
              -1 => '+0.000000',
              +3 => '   +0.000',
              +5 => '     +0.0',
              +7 => '       +0',
              +9 => '+1.000e+9',
             +99 => '+1.000e99',
          +99999 => '+1.00e999',
        );
        @exps2fmt= sort {$a<=>$b} keys %fmt4exp;
        $fullfmt= '%+14.7e'; # %+1.2345678e-99
    }

    sub Num2Str {
        my( $num )= @_;
        my $full= sprintf $fullfmt, $num;
        my( $sign, $one, $rest, $esign, $eabs )=
            $full =~ m<
                ^\s*
                ([-+]?)(\d)\.(\d*)
                [eE]([-+]?)(\d+)
                \s*$
            >x;
        my $exp= $esign . $eabs;
        my $fmt;
        for my $exp2fmt (  @exps2fmt  ) {
            if(  $exp <= $exp2fmt  ) {
                $fmt= $fmt4exp{$exp2fmt};
                last;
            }
        }
        my $str= $fmt;
        if(  $fmt =~ /e/  ) {
            $str =~ s/\+/$sign/;
            $str =~ s/1/$one/;
            $str =~ s{\.(0+)(?=[eE])}{
                (   sprintf( "%14.".length($1)."e", $num )
                        =~ /(\.\d+)/
                )[0]
            }e;
            $str =~ s/(9+)/sprintf "%0".length($1)."d", $eabs/e;
        } else {
            if(  $exp < 0  ) {
                $str =~ s/\+/$sign/;
                $rest= '0'x($eabs-1) . $one . $rest;
            } else {
                $one= substr( $one . $rest, 0, 1+$exp );
                substr( $rest, 0, $exp )= '';
                $str =~ s/([\s+0]+)/sprintf "%+".length($1)."s", $sign
+.$one/e;
            }
            $str =~ s{\.(0+)}{
                (   sprintf( "%14.".length($1)."f", $num )
                        =~ /(\.\d+)$/
                )[0]
            }e;
            $str =~ s{\.(0+)$}{
                (   sprintf( "%14.".length($1)."f", $num )
                        =~ /(\.\d+)/
                )[0]
            }e;
            $str =~ s/(\.?0+)$/' ' x length($1)/e
                if  $fmt =~ /\./;
        }
        return $str;
    }

}

sub Main {
    for my $exp (  -101..-98, -11, -10..11, 98..101  ) {
        for my $sign (  '', '-'  ) {
            my $num= 0 + ( $sign . "5.555555555e" . $exp );
            printf "%-20s (%s)\n", $num, Num2Str($num);
        }
    }
    for my $exp (  -10..11 ) {
        for my $sign (  '', '-'  ) {
            my $num= 0 + ( $sign . "1e" . $exp );
            printf "%-20s (%s)\n", $num, Num2Str($num);
            printf "%-20s (%s)\n", 0, Num2Str(0)
                if  1 == $num;
        }
    }
}

[download]

In reply to Display floating point numbers in compact, fixed-width format by tye

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.