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Math::Roman - Arbitrary sized Roman numbers and conversion from and to Arabic.


    use Math::Roman qw(roman);

    $a = new Math::Roman 'MCMLXXIII';  # 1973
    $b = roman('MCMLXI');              # 1961
    print $a - $b,"\n";                # prints 'XII'
    $d = Math::Roman->bzero();         # ''
    $d++;                              # 'I'  
    $d += 1998;                        # 'MCMXCIX'
    $d -= 'MCM';                       # 'XCIX'

    print "$d\n";                      # string       "MCMIC"
    print $d->as_number(),"\n";        # Math::BigInt "+1999"


perl5.005, Exporter, Math::BigInt


Exports nothing on default, but can export as_number(), roman(), and error().


Well, it seems I have been infected by the Perligata-Virus, too. ;o)

This module lets you calculate with Roman numbers, as if they were big integers. The numbers can have arbitrary length and all the usual functions from Math::BigInt are available.


The Roman single digits are as follows:

        I       1
        V       5
        X       10
        L       50
        C       100
        D       500
        M       1000

The following (quite modern) rules are in effect:

    Each of I, X and C can be repeated up to 3 times, V, L and D only once. Technically, M could be used up to four times, but this module imposes no limit on this to allow arbitrarily big numbers.

    A Roman number consists of tokens, each token is either a digit from IVXLCDM or consist of two digits, whereas the first digit is smaller than the second one. In the latter case the first digit is subtracted from the second (e.g. IV means 4, not 6).

    The smaller number must be a power of ten (I, X or C) and precede a number no larger than 10 times its own value. The smaller number itself can be preceded only by a number at least 10 times greater (e.g. LXC is invalid) and it must also be larger than any numeral that follows the one from which it is being subtracted (e.g. CMD is invalid).

    Each token must be smaller than the token before (e.g. IIV is invalid, since I is smaller than IV).

    The input will be checked and the result will be a 'NaN' if the check fails. You can get the cause with Math::Roman::error() until you try to create the next Roman number.

    The default list of valid tokens a Roman number can consist of is thus:

            III     3
            XXX     30
            CCC     300
            II      2
            XX      20
            CC      200
            IV      4
            IX      9
            XL      40
            XC      90
            CD      400
            CM      900
            I       1
            V       5
            X       10
            L       50
            C       100
            D       500
            M       1000

    The default list of invalid tokens is as follows:

            IIII            XXXX            CCCC
            DD              LL              VV              
            C[MD][CDM]      X[LC][XLCDM]    I[VX][IVXLCDM]  

Thanx must go to for clarifications.


The output will always be of the shortest possible form, and the tokens will be arranged in a decreasing order.


You can use Math::Roman::tokens() to get an array with all the defined tokens and their value. Tokens with a value of -1 are invalid, all others are valid. The format is token0, value0, token1, value1...

You can create your own set and store it with Math::Roman::tokens(). The routine expects an array of the form token, value, token, value... etc. Each token can be a simple string or regular expresion. Values of -1 indicate invalid tokens.

Here is an example that removes the subtraction (only addition is valid) as well as most of the other rules. It then parses 'XIIII' to be 14, then redefine the token set completely and parses 'AAB' to be 25:

            use Math::Roman;
            Math::Roman::tokens( qw(I 1  V 5  X 10  L 50  C 100  D 500  M 1000));
            $r = Math::Roman::roman('XIIII');
            print "'$r' is ",$r->as_number(),"\n";
            $r = Math::Roman::roman('XV');
            print "'$r' is ",$r->as_number(),"\n";
            Math::Roman::tokens ( qw(A 10 B 5) );
            $r = Math::Roman::roman('AAB');
            print "'$r' is ",$r->as_number(),"\n";

Another idea is to implement the dash over symbols, this indicates multiplying by 1000. Since it is hard to do this in ASCII, lower-case letters could be used like in the following:

        use Math::Roman;
        # will wrongly ommit the 'M's, but so much 'M's would not fit
        # on your screen anyway
        print 'old: ',new Math::Roman ('+12345678901234567890'),"\n";
        @a = Math::Roman::tokens();
        push @a, qw ( v 5000  x 10000  l 50000  c 100000  d 500000  
                      m 1000000 );
        print 'new: ',new Math::Roman ('+12345678901234567890'),"\n";




Create a new Math::Roman object. Argument is a Roman number as string, like 'MCMLXXIII' (1973) of the form /^[IVXLCDM]*$/ (see above for further rules) or a string number as used by Math::BigInt.



Just like new, but you can import it to write shorter code.



Return error of last number creation when result was NaN.



Return a string representing the internal value as a Roman number according to the aforementioned rules. A zero will be represented by ''. The output will only consist of valid tokens, and not contain a sign. Use as_number() if you need the sign.

This function always generates the shortest possible form.



Return a string representing the internal value as a normalized arabic number, including sign.


Uses internally Math::BigInt to do the math, all with overloaded operators.

Roman has neither negative numbers nor zero, but this module handles these, too. You will get only the absolute value as Roman number, but can look at the sign with sign() or use as_number().


  use Math::Roman qw(roman);

  print Math::Roman->new('MCMLXXII')->as_number(),"\n";
  print Math::Roman->new('LXXXI')->as_number(),"\n";
  print roman('MDCCCLXXXVIII')->as_number(),"\n";

  $a = roman('1311');
  print "$a is ",$a->as_number(),"\n";

  $a = roman('MCMLXXII');
  print "\$a is now $a (",$a->as_number(),")\n";
  $a++; $a += 'MCMXII'; $a = $a * 'X' - 'I';
  print "\$a is now $a (",$a->as_number(),")\n"; 


Internal Number Length

For the actual math, the same limits as in Math::BigInt apply.

Output length

The output in Roman is limited to 65536 times the biggest symbol. With the default set this is 'M', so the biggest Roman number you can print is 65536000 - and it will give you 64 KBytes M's in a row. This could be fixed, but who really needs it? ;)

Number Rules

The rule "Each token must be greater than the token before" is hard-coded in and can not be overcome. So 'IIX' will be invalid for subtraction-less numbers unless you define an 'IIX' token with a value of 12.


Importing functions

You can not import ordinary math functions like badd() and write things like:

        use Math::Roman qw(badd);               # will fail

        $a = badd('MCM','M');                   # does not work
        $a = Math::Roman::badd('MCM','M');      # neither

It is be possible to make this work, but this takes quite a lot of Copy&Paste code, and some small overhead price for every calculation. I think this is really not needed, since you can always use:

        use Math::Roman;

        $a = new Math::Roman 'MCM'; $a += 'M';  # neat isn't it?
        $a = Math::Roman->badd('MCM','M');      # or this
'0'-'9' as tokens

0-9 in the token set produce wrong results in new() if the given argument consists only of 0-9. That is because first a BigInt is tried to be constructed, and in this case, would succeed.


This program is free software; you may redistribute it and/or modify it under the same terms as Perl itself.


If you use this module in one of your projects, then please email me. I want to hear about how my code helps you ;)

Copyright (C) MCMXCIX-MMIV by Tels