costly move loop

0x000062ae      2 bset.b d3, d4
0x000062b0      4 lea.l (a1, d2.l), a6
0x000062b4      4 move.w 0x1ff, d3
; CODE XREF from fcn.000061d8 @ 0x62c6
0x000062b8      2 move.b (a0)+, d5
0x000062ba      4 move.b (a5, d5.w), d0
0x000062be      2 move.b (a0)+, d5
0x000062c0      4 or.b (a4, d5.w), d0
0x000062c4      2 move.b d0, (a6)+
0x000062c6      4 dbra d3, 0x62b8