/**
 * Reset internal tables. Used during benchmarking.
 */
export declare function _resetTables(): void;
/**
 * Calculate the smallest power of two greater or equal to the input value.
 * @param x Integer to compare to.
 * @returns Smallest `2**n` such that `x <= 2**n`.
 */
export declare function ceilPow2(x: number): number;
/**
 * Calculate the unnormalized forward discrete Fourier transform.
 * @param realIn Real components of the signal.
 * @param imagIn Imaginary components of the signal (all zeros assumed if missing).
 * @returns Array of [real coefficients, imaginary coefficients].
 */
export declare function fft(realIn: Float64Array, imagIn?: Float64Array): [Float64Array, Float64Array];
/**
 * Calculate the unnormalized reverse discrete Fourier transform.
 * @param realIn Real coefficients of a forward transform.
 * @param imagIn Imaginary coefficients of a forward transform.
 * @returns Array of [real signal, imaginary signal] scaled by the length of the original signal.
 */
export declare function ifft(realIn: Float64Array, imagIn: Float64Array): [Float64Array, Float64Array];
/**
 * Calculate the unnormalized reverse discrete Fourier transform.
 * @param realIn Real coefficients of a forward transform.
 * @param imagIn Imaginary coefficients of a forward transform.
 * @returns Real signal scaled by the length of the original signal.
 */
export declare function ifftReal(realIn: Float64Array, imagIn: Float64Array): Float64Array;