/**
 * Sum of array elements with optional NaN-skipping.
 * When `skipna` is true (default) NaNs are ignored; returns NaN if no valid samples.
 * Uses a fast dense path when global optimization allows it.
 * @param source Input array
 * @param skipna Whether to ignore NaNs (default: true)
 * @returns Sum or NaN
 */
export declare function sum(source: ArrayLike<number>, skipna?: boolean): number;
/**
 * Cumulative sum preserving NaNs: NaN entries do not increase the running sum
 * but are represented as the running total up to that point.
 * @param source Input array
 * @returns Float64Array of cumulative sums
 */
export declare function cumsum(source: ArrayLike<number>): Float64Array;
/**
 * Rolling sum over a window with optional NaN-skipping.
 * If `skipna` is true, windows with no valid values produce NaN.
 * Supports a fast dense path when inputs contain no NaNs.
 * @param source Input array
 * @param period Window length (must be > 0)
 * @param skipna Whether to ignore NaNs (default: true)
 * @returns Float64Array of rolling sums (NaN for positions before window fills)
 */
export declare function rollsum(source: ArrayLike<number>, period: number, skipna?: boolean): Float64Array;