php number to word code

public function numberToWord($number, $option = ['decimal' => 'dollar', 'fraction' => 'cents'])

    {

        $hyphen = '-';

        $conjunction = ' and ';

        $separator = ', ';

        $negative = 'negative ';

        $decimal = ' ' . $option['decimal'] . ' ';

        $afterFraction = $option['fraction'];

        $dictionary = array(0 => 'zero', 1 => 'one', 2 => 'two', 3 => 'three', 4 => 'four', 5 => 'five', 6 => 'six', 7 => 'seven', 8 => 'eight', 9 => 'nine', 10 => 'ten', 11 => 'eleven', 12 => 'twelve', 13 => 'thirteen', 14 => 'fourteen', 15 => 'fifteen', 16 => 'sixteen', 17 => 'seventeen', 18 => 'eighteen', 19 => 'nineteen', 20 => 'twenty', 30 => 'thirty', 40 => 'fourty', 50 => 'fifty', 60 => 'sixty', 70 => 'seventy', 80 => 'eighty', 90 => 'ninety', 100 => 'hundred', 1000 => 'thousand', 1000000 => 'million', 1000000000 => 'billion', 1000000000000 => 'trillion', 1000000000000000 => 'quadrillion', 1000000000000000000 => 'quintillion');

        if (!is_numeric($number)) {

            return false;

        }

        if (($number >= 0 && (int)$number < 0) || (int)$number < 0 - PHP_INT_MAX) {

            // overflow

            trigger_error('convert_number_to_words only accepts numbers between -' . PHP_INT_MAX . ' and ' . PHP_INT_MAX, E_USER_WARNING);

            return false;

        }

        if ($number < 0) {

            return $negative . $this->numberToWord(abs($number));

        }

        $string = $fraction = null;

        if (strpos($number, '.') !== false) {

            list($number, $fraction) = explode('.', $number);

        }

        switch (true) {

            case $number < 21:

                $string = $dictionary[$number];

                break;

            case $number < 100:

                $tens = ((int)($number / 10)) * 10;

                $units = $number % 10;

                $string = $dictionary[$tens];

                if ($units) {

                    $string .= $hyphen . $dictionary[$units];

                }

                break;

            case $number < 1000:

                $hundreds = $number / 100;

                $remainder = $number % 100;

                $string = $dictionary[$hundreds] . ' ' . $dictionary[100];

                if ($remainder) {

                    $string .= $conjunction . $this->numberToWord($remainder);

                }

                break;

            default:

                $baseUnit = pow(1000, floor(log($number, 1000)));

                $numBaseUnits = (int)($number / $baseUnit);

                $remainder = $number % $baseUnit;

                $string = $this->numberToWord($numBaseUnits) . ' ' . $dictionary[$baseUnit];

                if ($remainder) {

                    $string .= $remainder < 100 ? $conjunction : $separator;

                    $string .= $this->numberToWord($remainder);

                }

                break;

        }

        if (null !== $fraction && is_numeric($fraction)) {

            $string .= $decimal;

            $words = array();

            foreach (str_split((string)$fraction) as $number) {

                $words[] = $dictionary[$number];

            }

            $string .= implode(' ', $words) . " " . $afterFraction;

        }

        return $string;

    }