==== Here is the minimized test demonstrating the bug ====
import java.lang.Bignum;
class java_lang_Bignum_floatValue {
  public static void main(String args[]) {
    Bignum b=new Bignum(Float.MAX_VALUE, 0);
    System.out.println("b = " + b);
    System.out.println("b.floatValue() = " + b.floatValue());
    System.out.println("b.doubleValue() = " + b.doubleValue());
  }
}
==== Here is the output of the test ===
b = 340282346638528860000000000000000000000
b.floatValue() = 7.421703E+15
b.doubleValue() = 7.421703038235E+15