/**
 * Calculates the byte length of a base64 encoded string.
 * @param {string} string Base64 encoded string
 * @returns {number} Byte length
 */
export declare const length: (string: string) => number;
/**
 * Encodes a buffer to a base64 encoded string.
 * @param {Uint8Array} buffer Source buffer
 * @param {number} start Source start
 * @param {number} end Source end
 * @returns {string} Base64 encoded string
 */
export declare const encode: (buffer: Uint8Array, start: number, end: number) => string;
/**
 * Decodes a base64 encoded string to a buffer.
 * @param {string} string Source string
 * @param {Uint8Array} buffer Destination buffer
 * @param {number} offset Destination offset
 * @returns {number} Number of bytes written
 * @throws {Error} If encoding is invalid
 */
export declare const decode: (string: string, buffer: Uint8Array, offset: number) => number;
/**
 * Tests if the specified string appears to be base64 encoded.
 * @param {string} string String to test
 * @returns {boolean} `true` if probably base64 encoded, otherwise false
 */
export declare const test: (string: string) => boolean;