void swapBufferHalves( U8 *buf, U32 start, U32 length ) {
    register U64 *p1 = (U64*)&buf[ start ];
    register U64 *p2 = (U64*)&buf[ start + ( length >> 1 ) ];
    const U64 *pend = (U64*)(start + length);
    register U64 temp;

	assert( !( length & 1 ) );
	assert( ( (U64)buf & 7ull ) == 0 );

    while( p1 < pend ) {
         temp = *p1;
         *p1++ = *p2;
         *p2++ = temp;
    }
    return;
}