message.js

function buildMessage(values) {
  const DIFF = Math.pow(2, 9); // 512
  const MAX_PRECISION = 4; // 512 * 4 allows to encode 300 <= x <= 1100
  const maxIndex = values.indexOf(Math.max(...values));
  const minIndex = values.indexOf(Math.min(...values));
  const maxDiff = values.reduce(
    (diff, v) => Math.max(v - values[minIndex], diff),
    0
  );
  const precision = Math.ceil(maxDiff / DIFF);

  if (precision > MAX_PRECISION) {
    throw new Error('Cannot encode to that precision' + precision);
  }

  return JSON.stringify({
    min: Math.round(values[minIndex]),
    maxDiff: Math.round((values[maxIndex] - values[minIndex]) / precision),
    leftDiffs: 
      values
        .filter((v, index) => index !== maxIndex && index !== minIndex)
        .map(v => Math.round(v - values[minIndex])),
    precision, // 1 or 2 bits
    minIndex, // max values.length bits
    maxIndex, // max values.length bits
  }, null, 2);
}