function typedarray( ctor, len, dtype ) {
		var buf;
		if ( len === 0 ) {
			return new ctor( 0 );
		}
		buf = arraybuffer( ceil2( len )*BYTES_PER_ELEMENT[ dtype ] );
		if ( buf === null ) {
			return buf;
		}
		return new ctor( buf, 0, len );
	}
Returns a typed array.

@private
@param {Function} ctor - typed array constructor
@param {NonNegativeInteger} len - view length
@param {string} dtype - data type
@returns {(TypedArray|null)} typed array or null