Converts decimal numbers to Roman numerials. Limit [1; 3999]

DecimalToRoman.php

<?php
/**
 * Converts decimal numbers to Roman numerials.
 * Limit [1; 3999]
 * 
 * @param  integer $n
 * @param  bool $recursive
 * @return string
 */
function decroman($n, $recursive = false) {
    if( !($n > 0 && $n < 4000))
        return;

    $roman = array(
        1    => 'I',
        4    => 'IV',
        5    => 'V',
        9    => 'IX',
        10   => 'X',
        40   => 'XL',
        50   => 'L',
        90   => 'XC',
        100  => 'C',
        400  => 'CD',
        500  => 'D',
        900  => 'CM',
        1000 => 'M',
    );

    if(array_key_exists($n, $roman))
        return $roman[$n];

    if($n < 10 || $n % 10 === 0 || $n % 100 === 0 || $n % 1000 === 0) {
        for($m = 1; $m <= 1000; $m *= 10) {
            for($i = 2; $i < 4; $i++)
                if($n / $m === $i)
                    return str_repeat($roman[$n / $i], $i);

            for($i = 6; $i < 9; $i++)
                if($n / $m === $i)
                    return $roman[$n - abs($i - 5) * $m] . decrom($n / $i * ($i - 5));
        }
    }

    if(!$recursive) {
        $roman = array();
        $roman = '';
        $ten = 1;
        do {
            $roman[] = decrom(($n % 10) * $ten, true);
            $n = (int) ($n / 10);
            $ten = $ten * 10;
        } while ($n > 0);

        return implode('', array_reverse($roman));
    }
}