a3=(_Q15)((long)a1*(int)a2>>15);
0552 90001E mov.w [0x001c+2],0x0000
0554 B90161 mul.su 0x0000,#1,0x0004
0556 90002E mov.w [0x001c+4],0x0000
0558 DE80CF asr 0x0000,#15,0x0002
055A B99A00 mul.ss 0x0006,0x0000,0x0008
055C 780204 mov.w 0x0008,0x0008
055E B98B02 mul.ss 0x0002,0x0004,0x000c
0560 780286 mov.w 0x000c,0x000a
0562 420205 add.w 0x0008,0x000a,0x0008
0564 B81000 mul.uu 0x0004,0x0000,0x0000
0566 420201 add.w 0x0008,0x0002,0x0008
0568 780084 mov.w 0x0008,0x0002
056A DD0941 sl 0x0002,#1,0x0004
056C DE004F lsr 0x0000,#15,0x0000
056E 710000 ior.w 0x0004,0x0000,0x0000
0570 DE88CF asr 0x0002,#15,0x0002
0572 780F00 mov.w 0x0000,[0x001c]