code: public static double floorPowerOfBdouble(final double b, final double n) {
      final double x = (n < 1.0) ? 1.0 : n;
      return pow(b, floor(logB(b, x)));
    }
docs: Computes the floor power of B as a double. This is the largest positive power
  of B that equal to or less than the given n and equal to a mathematical integer.
  The result of this function is consistent with {@link #floorPowerOf2(int)} for values
  less than one. I.e., if <i>n &lt; 1,</i> the result is 1.
  
  @param b The base in the expression &#8970;b<sup>n</sup>&#8971;.
  @param n The input argument.
  @return the floor power of 2 and equal to a mathematical integer.