<?php
// Function that calculates the roman string to the given number:
function dec2roman($f)
{
 // Return false if either $f is not a real number, 
 //$f is bigger than 3999 or $f is lower or equal to 0:  
  if(!is_numeric($f) || $f > 3999 || $f <= 0) return false;
 // Define the roman figures:
  $roman = array(
  'M' => 1000,
  'D' => 500,
  'C' => 100,
  'L' => 50,
  'X' => 10,
  'V' => 5,
  'I' => 1
  );
 // Calculate the needed roman figures:
  foreach($roman as $k => $v)
  if(($amount[$k] = floor($f / $v)) > 0)
  $f -= $amount[$k] * $v;
 // Build the string:
  $return = '';
  foreach($amount as $k => $v)
  {
   $return .= $v <= 3 ? str_repeat($k, $v) : $k . $old_k;
   $old_k = $k;  
  }
 // Replace some spacial cases and return the string:
  return str_replace(array('VIV','LXL','DCD'),array('IX','XC','CM'),$return);
}
// echo dec2romen(1981);
// Function to get the decimal value of a roman string:
function roman2dec($str = '')
{
 // Return false if not at least one letter is in the string:
  if(is_numeric($str)) return false;
 // Define the roman figures:
  $roman = array(
  'M' => 1000,
  'D' => 500,
  'C' => 100,
  'L' => 50,
  'X' => 10,
  'V' => 5,
  'I' => 1
  );
 // Convert the string to an array of roman values:
  for($i = 0; $i < strlen($str); $i++) 
  if(isset($roman[strtoupper($str[$i])]))
  $values[] = $roman[strtoupper($str[$i])];
 // Calculate the sum of that array:
  $sum = 0;
  while($current = current($values))
  {
   $next = next($values);
   $next > $current ? $sum += $next - $current + 0 * next($values) : $sum += $current;
  }
 // Return the value:
  return $sum;
}
// echo roman2dec(IX);  
?>