Formatting numbers

Hi!

Is there a function for formatting numbers by inserting characters like ,
and .?
If there isn't, does someone feel like writing it? :)
I have something like the following in mind:

str_format_number($number, $character, $every [, $maxnumber])

To illustrate what it would do, here are some examples:

            str_format_number(10000, ',', 3) := "100,00"
         str_format_number(12345678, ',', 3) := "123,456,78"
        str_format_number(12345678, ',', -3) := "12,345,678"
str_format_number(1234567890123, ',', -3, 2) := "1234567,890,123"
        str_format_number(12345, '.', -2, 1) := "123.45"
 str_format_number(1234567890123456, ' ', 4) := "1234 5678 9012 3456"

$number is the number to format
$character is the string to insert
$every specifies how many numbers to group together. Negative $every means
the function should start at the end.
$maxnumber is the maximum number of $character's to insert..


thanks,
Mitja