===== Here is the minimized test demonstrating the bug =====
import java.lang.Bignum;
class java_lang_Bignum_remainder {

  public static void main(String args[]) {
    Bignum b=new Bignum("-912098539475.412556321");
    System.out.println(Bignum.ZERO.remainder(b));
  }
}
===== Here is the output of the test =====
java.lang.NegativeArraySizeException
at java.lang.Bignum._intDivide(Bignum.java)
at java.lang.Bignum.remainder(Bignum.java)
at java_lang_Bignum_remainder.main(java_lang_Bignum_remainder.java:6)