Toptal Codility Problem: Convert to-and-from base -2

base-neg-2.js

'use strict';

function toDecimal(A) {
  var sum = 0;
  for (var i = 0; i < A.length; i++) {
    sum += A[i] * Math.pow(-2, i);
  }
  return sum;
}

function toBaseNeg2(d) {
  var a = [];
  while (d != 0) {
    var remainder = d % -2;
    var d = Math.ceil(d / -2);
    a.push(Math.abs(remainder));
  }
  return a;
}

function solution(A, B) {
  var d = toDecimal(A);
  return toBaseNeg2(-d);
}

console.log(toDecimal([1,0,0,1,1])     === 9);
console.log(toDecimal([1,1,0,1])       === -9);
console.log(toDecimal([1,0,0,1,1,1])   === -23);
console.log(toDecimal([1,1,0,1,0,1,1]) === 23);

console.log(JSON.stringify(toBaseNeg2(9))   == JSON.stringify([1,0,0,1,1]));
console.log(JSON.stringify(toBaseNeg2(-9))  == JSON.stringify([1,1,0,1]));
console.log(JSON.stringify(toBaseNeg2(-23)) == JSON.stringify([1,0,0,1,1,1]));
console.log(JSON.stringify(toBaseNeg2(23))  == JSON.stringify([1,1,0,1,0,1,1]));