Function roundNumber

packages/common/src/i18n/format_number.ts:461–533

* Round the parsed number to the specified number of decimal places * This function changes the parsedNumber in-place

(parsedNumber: ParsedNumber, minFrac: number, maxFrac: number)

 * This function changes the parsedNumber in-place
 */
function roundNumber(parsedNumber: ParsedNumber, minFrac: number, maxFrac: number) {
  if (minFrac > maxFrac) {
    throw new RuntimeError(
      RuntimeErrorCode.INVALID_NUMBER_OF_DIGITS_AFTER_FRACTION,
      ngDevMode &&
        `The minimum number of digits after fraction (${minFrac}) is higher than the maximum (${maxFrac}).`,
    );
  }

  let digits = parsedNumber.digits;
  let fractionLen = digits.length - parsedNumber.integerLen;
  const fractionSize = Math.min(Math.max(minFrac, fractionLen), maxFrac);

  // The index of the digit to where rounding is to occur
  let roundAt = fractionSize + parsedNumber.integerLen;
  let digit = digits[roundAt];

  if (roundAt > 0) {
    // Drop fractional digits beyond `roundAt`
    digits.splice(Math.max(parsedNumber.integerLen, roundAt));

    // Set non-fractional digits beyond `roundAt` to 0
    for (let j = roundAt; j < digits.length; j++) {
      digits[j] = 0;
    }
  } else {
    // We rounded to zero so reset the parsedNumber
    fractionLen = Math.max(0, fractionLen);
    parsedNumber.integerLen = 1;
    digits.length = Math.max(1, (roundAt = fractionSize + 1));
    digits[0] = 0;
    for (let i = 1; i < roundAt; i++) digits[i] = 0;
  }

  if (digit >= 5) {
    if (roundAt - 1 < 0) {
      for (let k = 0; k > roundAt; k--) {
        digits.unshift(0);
        parsedNumber.integerLen++;
      }
      digits.unshift(1);
      parsedNumber.integerLen++;
    } else {
      digits[roundAt - 1]++;
    }
  }

  // Pad out with zeros to get the required fraction length
  for (; fractionLen < Math.max(0, fractionSize); fractionLen++) digits.push(0);

  let dropTrailingZeros = fractionSize !== 0;
  // Minimal length = nb of decimals required + current nb of integers
  // Any number besides that is optional and can be removed if it's a trailing 0
  const minLen = minFrac + parsedNumber.integerLen;
  // Do any carrying, e.g. a digit was rounded up to 10
  const carry = digits.reduceRight(function (carry, d, i, digits) {
    d = d + carry;
    digits[i] = d < 10 ? d : d - 10; // d % 10