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A general-purpose Scala utility library

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package grizzled

/** Useful binary-related utility functions.
  */
object binary {

  /** Count the number of bits in a numeric (integer or long) value. This
    * method is adapted from the Hamming Weight algorithm. It works for
    * up to 64 bits.
    *
    * @param num  the numeric value
    *
    * @return the number of 1 bits in a binary representation of `num`
    */
  def bitCount(num: Int): Int = {
    val numLong: Long = num.toLong
    bitCount(numLong & 0xffffffffL)
  }

  /** Count the number of bits in a numeric (integer or long) value. This
    * method is adapted from the Hamming Weight algorithm. It works for
    * up to 64 bits.
    *
    * @param num  the numeric value
    *
    * @return the number of 1 bits in a binary representation of `num`
    */
  def bitCount(num: Long): Int = {
    // Put count of each 2 bits into those 2 bits.
    val res1: Long = num - ((num >> 1) & 0x5555555555555555L)

    // Put count of each 4 bits into those 4 bits.
    val allThrees = 0x3333333333333333L
    val res2 = (res1 & allThrees) + ((res1 >> 2) & allThrees)

    // Put count of each 8 bits into those 8 bits.
    val res3 = (res2 + (res2 >> 4)) & 0x0f0f0f0f0f0f0f0fL

    // Left-most bits.
    ((res3 * 0x0101010101010101L) >> 56).toInt
  }
}