PDP-11 sample problem answer

1a. It computes [X]² - [Y]² and puts the result in W, unless one of the squaring operations yields a result greater than or equal to 2¹⁶ in which case it puts the value 0 in W.

1b.

1000 016702 MOV X, R2

1002 000044

1004 070267 MUL X, R2

1006 000040

1010 005703 TST R3

1012 001012 BNE OVERFLOW

1014 016704 MOV Y, R4

1016 000032

1020 070467 MUL Y, R4

1022 000026

1024 005705 TST R5

1026 001004 BNE OVERFLOW

1030 160402 SUB R4, R2

1032 010267 MOV R2, W

1034 000016

1036 000000 HALT

1040 012767 MOV #0, W

1042 000000

1044 000006

1046 000000 HALT

1050 000022 .WORD 22

1052 000033 .WORD 33

1054 000000 .WORD 0

[on to problem #2]

1000	016702	MOV X, R2
1002	000044
1004	070267	MUL X, R2
1006	000040
1010	005703	TST R3
1012	001012	BNE OVERFLOW
1014	016704	MOV Y, R4
1016	000032
1020	070467	MUL Y, R4
1022	000026
1024	005705	TST R5
1026	001004	BNE OVERFLOW
1030	160402	SUB R4, R2
1032	010267	MOV R2, W
1034	000016
1036	000000	HALT
1040	012767	MOV #0, W
1042	000000
1044	000006
1046	000000	HALT
1050	000022	.WORD 22
1052	000033	.WORD 33
1054	000000	.WORD 0