How to use

floorLog2

method

in

javolution.lang.MathLib

/**
 * Returns the largest power of 2 that is less than or equal to the
 * the specified positive value.
 *
 * @param d the <code>double</code> number.
 * @return <code>floor(Log2(abs(d)))</code>
 * @throws ArithmeticException if <code>d &lt;= 0<code> or <code>d</code>
 *         is <code>NaN</code> or <code>Infinity</code>.
 **/
public static int floorLog2(double d) {
  if (d <= 0)
    throw new ArithmeticException("Negative number or zero");
  long bits = Double.doubleToLongBits(d);
  int exp = ((int) (bits >> 52)) & 0x7FF;
  if (exp == 0x7FF)
    throw new ArithmeticException("Infinity or NaN");
  if (exp == 0)
    return floorLog2(d * 18014398509481984L) - 54; // 2^54 Exact.       
  return exp - 1023;
}

/**
 * Returns the largest power of 2 that is less than or equal to the
 * the specified positive value.
 *
 * @param d the <code>double</code> number.
 * @return <code>floor(Log2(abs(d)))</code>
 * @throws ArithmeticException if <code>d &lt;= 0<code> or <code>d</code>
 *         is <code>NaN</code> or <code>Infinity</code>.
 **/
public static int floorLog2(double d) {
  if (d <= 0)
    throw new ArithmeticException("Negative number or zero");
  long bits = Double.doubleToLongBits(d);
  int exp = ((int) (bits >> 52)) & 0x7FF;
  if (exp == 0x7FF)
    throw new ArithmeticException("Infinity or NaN");
  if (exp == 0)
    return floorLog2(d * 18014398509481984L) - 54; // 2^54 Exact.       
  return exp - 1023;
}

/**
 * Returns the largest power of 2 that is less than or equal to the
 * the specified positive value.
 *
 * @param d the <code>double</code> number.
 * @return <code>floor(Log2(abs(d)))</code>
 * @throws ArithmeticException if <code>d &lt;= 0<code> or <code>d</code>
 *         is <code>NaN</code> or <code>Infinity</code>.
 **/
public static int floorLog2(double d) {
  if (d <= 0)
    throw new ArithmeticException("Negative number or zero");
  long bits = Double.doubleToLongBits(d);
  int exp = ((int) (bits >> 52)) & 0x7FF;
  if (exp == 0x7FF)
    throw new ArithmeticException("Infinity or NaN");
  if (exp == 0)
    return floorLog2(d * 18014398509481984L) - 54;  // 2^54 Exact.       
  return exp - 1023;
}
/**/

/**
 * Returns the largest power of 2 that is less than or equal to the
 * the specified positive value.
 *
 * @param d the <code>double</code> number.
 * @return <code>floor(Log2(abs(d)))</code>
 * @throws ArithmeticException if <code>d &lt;= 0<code> or <code>d</code>
 *         is <code>NaN</code> or <code>Infinity</code>.
 **/
public static int floorLog2(double d) {
  if (d <= 0)
    throw new ArithmeticException("Negative number or zero");
  long bits = Double.doubleToLongBits(d);
  int exp = ((int) (bits >> 52)) & 0x7FF;
  if (exp == 0x7FF)
    throw new ArithmeticException("Infinity or NaN");
  if (exp == 0)
    return floorLog2(d * 18014398509481984L) - 54; // 2^54 Exact.       
  return exp - 1023;
}

/**
 * Returns the largest power of 10 that is less than or equal to the
 * the specified positive value.
 *
 * @param d the <code>double</code> number.
 * @return <code>floor(Log10(abs(d)))</code>
 * @throws ArithmeticException if <code>d &lt;= 0<code> or <code>d</code>
 *         is <code>NaN</code> or <code>Infinity</code>.
 **/
public static int floorLog10(double d) {
  int guess = (int) (LOG2_DIV_LOG10 * MathLib.floorLog2(d));
  double pow10 = MathLib.toDoublePow10(1, guess);
  if ((pow10 <= d) && (pow10 * 10 > d))
    return guess;
  if (pow10 > d)
    return guess - 1;
  return guess + 1;
}

/**
 * Returns the largest power of 10 that is less than or equal to the
 * the specified positive value.
 *
 * @param d the <code>double</code> number.
 * @return <code>floor(Log10(abs(d)))</code>
 * @throws ArithmeticException if <code>d &lt;= 0<code> or <code>d</code>
 *         is <code>NaN</code> or <code>Infinity</code>.
 **/
public static int floorLog10(double d) {
  int guess = (int) (LOG2_DIV_LOG10 * MathLib.floorLog2(d));
  double pow10 = MathLib.toDoublePow10(1, guess);
  if ((pow10 <= d) && (pow10 * 10 > d))
    return guess;
  if (pow10 > d)
    return guess - 1;
  return guess + 1;
}

/**
 * Returns the largest power of 10 that is less than or equal to the
 * the specified positive value.
 *
 * @param d the <code>double</code> number.
 * @return <code>floor(Log10(abs(d)))</code>
 * @throws ArithmeticException if <code>d &lt;= 0<code> or <code>d</code>
 *         is <code>NaN</code> or <code>Infinity</code>.
 **/
public static int floorLog10(double d) {
  int guess = (int) (LOG2_DIV_LOG10 * MathLib.floorLog2(d));
  double pow10 = MathLib.toDoublePow10(1, guess);
  if ((pow10 <= d) && (pow10 * 10 > d))
    return guess;
  if (pow10 > d)
    return guess - 1;
  return guess + 1;
}
private static final double LOG2_DIV_LOG10 = 0.3010299956639811952137388947;

/**
 * Returns the largest power of 10 that is less than or equal to the
 * the specified positive value.
 *
 * @param d the <code>double</code> number.
 * @return <code>floor(Log10(abs(d)))</code>
 * @throws ArithmeticException if <code>d &lt;= 0<code> or <code>d</code>
 *         is <code>NaN</code> or <code>Infinity</code>.
 **/
public static int floorLog10(double d) {
  int guess = (int) (LOG2_DIV_LOG10 * MathLib.floorLog2(d));
  double pow10 = MathLib.toDoublePow10(1, guess);
  if ((pow10 <= d) && (pow10 * 10 > d))
    return guess;
  if (pow10 > d)
    return guess - 1;
  return guess + 1;
}