scale is incorrect, decimal point position is wrong:
==== here is the minimized test ====
class java_lang_Bignum_constructor_1 {
  public static void main(String args[]) {
    System.out.println(new java.lang.Bignum(Double.MIN_VALUE,500));
  }
}
==== here is the output of the test ====
4900000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.0