Function numberToExpression

src/compute-engine/numerics/expression.ts:34–63

(
  num: number | bigint,
  fractionalDigits?: string | number
)

/** Output a shorthand if possible */
export function numberToExpression(
  num: number | bigint,
  fractionalDigits?: string | number
): MathJsonExpression {
  if (typeof num === 'number') {
    if (isNaN(num)) return 'NaN';
    if (!Number.isFinite(num))
      return num < 0 ? 'NegativeInfinity' : 'PositiveInfinity';

    if (typeof fractionalDigits === 'number')
      return { num: num.toFixed(fractionalDigits) };

    return num;
  }

  if (num >= Number.MIN_SAFE_INTEGER && num <= Number.MAX_SAFE_INTEGER)
    return Number(num);

  // Only use the machine-number shorthand when the float is *exactly* equal to
  // the integer. A string-display comparison is unsound: e.g.
  // `Number(10n ** 23n).toString() === '1e+23'` is true because
  // `Number.prototype.toString()` returns the shortest uniquely-identifying
  // decimal, yet the float ≠ 10^23. Emitting that float as a JSON number would
  // corrupt the value on reconstruction. `BigInt(n)` of an integral float is
  // its exact value, so equality guarantees losslessness.
  const n = Number(num);
  if (Number.isFinite(n) && BigInt(n) === num) return n;

  return { num: numberToString(num) };
}