code: public static BigDecimal bigSqrt(final BigDecimal c) {
          if (c == null) {
              return null;
          }
  
          return c.signum() == 0 ? BigDecimal.ZERO : sqrtNewtonRaphson(c, BigDecimal.ONE, BigDecimal.ONE.divide(SQRT_PRE));
      }
docs: Uses Newton Raphson to compute the square root of a BigDecimal.
  
  @param c the BigDecimal for which we want the SQRT.
  @author Luciano Culacciatti
  @see <a href="http://www.codeproject.com/Tips/257031/Implementing-SqrtRoot-in-BigDecimal">http://www.codeproject.com/Tips/257031/Implementing-SqrtRoot-in-BigDecimal</a>