javascript to convert rule integer for life-like cellular automata to it's black/white reversal ruleset

life-like-cellular-automata-black-white-reversal.js

//https://www.conwaylife.com/wiki/Rule_integer
//https://www.conwaylife.com/wiki/Black/white_reversal

var rule_integer = 6152; // conway's game of life

function reverse_bits(bits, size) {
  let i = 0
  let reversed = 0
  let last
  while (i < size) {
    last = bits & 1
    bits >>= 1
    reversed += last
    reversed <<= 1
    i++
  }
  return reversed >> 1
}

function ruleint_to_string(rule_integer) {
  var birth_rules = rule_integer & 511; //(2^9)-1
  var survive_rules = rule_integer >>> 9;
  var birth_string = "B";
  var survive_string = "S";
  for (var string_bit = 0; string_bit < 9; string_bit++) {
    var bit_mask = Math.pow(2, string_bit);
    if ((bit_mask & birth_rules) > 0) {
      birth_string += string_bit;
    }
    if ((bit_mask & survive_rules) > 0) {
      survive_string += string_bit;
    }
  }
  return birth_string + "/" + survive_string;
}

function ruleint_black_white_reversal(rule_integer) {
  var birth_rules = rule_integer & 511; //(2^9)-1
  var survive_rules = rule_integer >>> 9;
	birth_rules ^= 511; //(2^9)-1
	survive_rules ^= 511; //(2^9)-1
  birth_rules = reverse_bits(birth_rules, 9);
  survive_rules = reverse_bits(survive_rules, 9);
  return (birth_rules << 9) + survive_rules;
}

console.log(ruleint_to_string(ruleint_black_white_reversal(rule_integer)));