Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Calculation/Statistical.php
public static function CHIDIST($value, $degrees)
    {
        $value = Functions::flattenSingleValue($value);
        $degrees = floor(Functions::flattenSingleValue($degrees));

        if ((is_numeric($value)) && (is_numeric($degrees))) {
            if ($degrees < 1) {
                return Functions::NAN();
            }
            if ($value < 0) {
                if (Functions::getCompatibilityMode() == Functions::COMPATIBILITY_GNUMERIC) {
                    return 1;
                }

                return Functions::NAN();
            }

            return 1 - (self::incompleteGamma($degrees / 2, $value / 2) / self::gamma($degrees / 2));
        }

        return Functions::VALUE();
    }
public static function CHIDIST($value, $degrees)
    {
        $value = Functions::flattenSingleValue($value);
        $degrees = floor(Functions::flattenSingleValue($degrees));

        if ((is_numeric($value)) && (is_numeric($degrees))) {
            if ($degrees < 1) {
                return Functions::NAN();
            }
            if ($value < 0) {
                if (Functions::getCompatibilityMode() == Functions::COMPATIBILITY_GNUMERIC) {
                    return 1;
                }

                return Functions::NAN();
            }

            return 1 - (self::incompleteGamma($degrees / 2, $value / 2) / self::gamma($degrees / 2));
        }

        return Functions::VALUE();
    }
CHIDIST.

Returns the one-tailed probability of the chi-squared distribution.

@param float $value Value for the function
@param float $degrees degrees of freedom

@return float