```ts

/**
 * a divided by b.
 *
 * This function throws:
 * - Error if either argument is NaN.
 * - Error if the divisor is zero (including -0).
 */
export function safeDivide(a: number, b: number): number {
  if (!isFinite(a) || !isFinite(b)) {
    throw new Error("Both arguments must be finite numbers.");
  }

  if (b === 0) {
    throw new Error("Division by zero is not allowed.");
  }

  return a / b;
}
```