export type Quat = readonly [number, number, number, number];
export declare function mul(a: Quat, b: Quat): [number, number, number, number];
/** Inverse of a unit quaternion (conjugate). */
export declare const conj: (q: Quat) => [number, number, number, number];
export declare function normalize(q: Quat): [number, number, number, number];
/** Quaternion from the upper-3x3 of a column-major matrix (assumed a pure rotation). three.js algorithm. */
export declare function fromMat(m: readonly number[]): [number, number, number, number];
/** Rotate a 3-vector by a unit quaternion (q · v · q⁻¹). */
export declare function rotateVec(q: Quat, v: readonly [number, number, number]): [number, number, number];
/** Spherical linear interpolation with double-cover (shortest-arc) handling. */
export declare function slerp(a: Quat, b: Quat, t: number): [number, number, number, number];
/** Sample a rotation track (sorted `times`, flat VEC4 `quats`) at time `t` with slerp. */
export declare function sampleQuat(times: ArrayLike<number>, quats: ArrayLike<number>, t: number): [number, number, number, number];
/** Sample a VEC3 track (translation) at time `t` with linear interpolation. */
export declare function sampleVec3(times: ArrayLike<number>, vals: ArrayLike<number>, t: number): [number, number, number];