PHP number to word converter using Indian numbering system

I was faced with a requirement to convert number to words/string in Indian naming system with lakhs and crores. I had to generate the amount in words for printing it out on a bill. The total amount, provided to the customer, needed to be converted to string. For example, if 1345673 was to be converted to Thirteen lakh Forty Five Thousand Six Hundred and Seventy Three, these functions will have to be followed.

Code is given below

/**
 * Function to convert a number to a the string literal for the number
 */
function getStringOfAmount($num) {
  $count = 0;
  global $ones, $tens, $triplets;
  $ones = array(
    '',
    ' One',
    ' Two',
    ' Three',
    ' Four',
    ' Five',
    ' Six',
    ' Seven',
    ' Eight',
    ' Nine',
    ' Ten',
    ' Eleven',
    ' Twelve',
    ' Thirteen',
    ' Fourteen',
    ' Fifteen',
    ' Sixteen',
    ' Seventeen',
    ' Eighteen',
    ' Nineteen'
  );
  $tens = array(
    '',
    '',
    ' Twenty',
    ' Thirty',
    ' Forty',
    ' Fifty',
    ' Sixty',
    ' Seventy',
    ' Eighty',
    ' Ninety'
  );

  $triplets = array(
    '',
    ' Thousand',
    ' Million',
    ' Billion',
    ' Trillion',
    ' Quadrillion',
    ' Quintillion',
    ' Sextillion',
    ' Septillion',
    ' Octillion',
    ' Nonillion'
  );
  return convertNum($num);
}

/**
 * Function to dislay tens and ones
 */
function commonloop($val, $str1 = '', $str2 = '') {
  global $ones, $tens;
  $string = '';
  if ($val == 0)
    $string .= $ones[$val];
  else if ($val < 20)
    $string .= $str1.$ones[$val] . $str2;  
  else
    $string .= $str1 . $tens[(int) ($val / 10)] . $ones[$val % 10] . $str2;
  return $string;
}

/**
 * returns the number as an anglicized string
 */
function convertNum($num) {
  $num = (int) $num;    // make sure it's an integer

  if ($num < 0)
    return 'negative' . convertTri(-$num, 0);

  if ($num == 0)
    return 'Zero';
  return convertTri($num, 0);
}

/**
 * recursive fn, converts numbers to words
 */
function convertTri($num, $tri) {
  global $ones, $tens, $triplets, $count;
  $test = $num;
  $count++;
  // chunk the number, ...rxyy
  // init the output string
  $str = '';
  // to display hundred & digits
  if ($count == 1) {
    $r = (int) ($num / 1000);
    $x = ($num / 100) % 10;
    $y = $num % 100;
    // do hundreds
    if ($x > 0) {
      $str = $ones[$x] . ' Hundred';
      // do ones and tens
      $str .= commonloop($y, ' and ', '');
    }
    else if ($r > 0) {
      // do ones and tens
      $str .= commonloop($y, ' and ', '');
    }
    else {
      // do ones and tens
      $str .= commonloop($y);
    }
  }
  // To display lakh and thousands
  else if($count == 2) {
    $r = (int) ($num / 10000);
    $x = ($num / 100) % 100;
    $y = $num % 100;
    $str .= commonloop($x, '', ' Lakh ');
    $str .= commonloop($y);
    if ($str != '')
      $str .= $triplets[$tri];
  }
  // to display till hundred crore
  else if($count == 3) {
    $r = (int) ($num / 1000);
    $x = ($num / 100) % 10;
    $y = $num % 100;
    // do hundreds
    if ($x > 0) {
      $str = $ones[$x] . ' Hundred';
      // do ones and tens
      $str .= commonloop($y,' and ',' Crore ');
    }
    else if ($r > 0) {
      // do ones and tens
      $str .= commonloop($y,' and ',' Crore ');
    }
    else {
      // do ones and tens
      $str .= commonloop($y);
    }
  }
  else {
    $r = (int) ($num / 1000);
  }
  // add triplet modifier only if there
  // is some output to be modified...
  // continue recursing?
  if ($r > 0)
    return convertTri($r, $tri+1) . $str;
  else
    return $str;
}