class Interpolation {
 static Linear( v, k ) {
   var m = v.length - 1,
       f = m * k,
       i = f.floor(),
       fn = _InterpolationUtils.Linear;

   if ( k < 0 ) return fn( v[ 0 ], v[ 1 ], f );
   if ( k > 1 ) return fn( v[ m ], v[ m - 1 ], m - f );

   return fn( v[ i ], v[ i + 1 > m ? m : i + 1 ], f - i );

 }
}