Automattic / jetpack

	 *

	 * @param String $password the password.

	 */

	protected function calculate_entropy_bits( $password ) {

		$bits          = 0;

		$charset_score = log( $this->get_charset_size( $password ) ) / log( 2 );

		$aidx   = $this->get_char_index( $password[0] );

		$length = strlen( $password );

		for ( $b = 1; $b < $length; $b++ ) {

			$bidx = $this->get_char_index( $password[ $b ] );

			// 27 = number of chars in the index (a-z,' ').

			$c     = 1.0 - $this->frequency_table[ $aidx * 27 + $bidx ];

			$bits += $charset_score * $c * $c;

			// Move on to next pair.

			$aidx = $bidx;

		}

		return $bits;

	}

	/**

	 * A frequency table of character pairs, starting with  '  ' then  ' a', ' b' [...] , 'a ', 'aa' etc.

	 *

	 * @return float|int

	 */

	protected function calculate_entropy_bits( $password ) {

		$bits = 0;

		// Calculate the score.

		$charset_score = log( $this->get_charset_size( $password ) ) / log( 2 );

		$aidx   = $this->get_char_index( $password[0] );

		$length = strlen( $password );

		for ( $b = 1; $b < $length; $b ++ ) {

			$bidx = $this->get_char_index( $password[ $b ] );

			// 27 = number of chars in the index (a-z,' ').

			$c = 1.0 - $this->frequency_table[ $aidx * 27 + $bidx ];

			// Increment the bits.

			$bits += $charset_score * $c * $c;

			// Move on to next pair.

			$aidx = $bidx;

		}

		return $bits;

	}