```ts
/** a divided by b. */
export function safeDivide(a: number, b: number): number {
  if (!Number.isFinite(a)) {
    throw new Error('Dividend must be a finite number');
  }
  if (!Number.isFinite(b)) {
    throw new Error('Divisor must be a finite number');
  }
  if (b === 0 || b === -0) {
    throw new Error('Division by zero is not allowed');
  }
  return a / b;
}
```