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jotd · 25 May 2022, 16:39

Question:

I have this '020 code

Code:

     moveq.l     #127,d5
     moveq.l     #126,d3
     move.l     (a0,d5.l*4),d0
     sub.l (a0,d3.l*4),d0

as d5 and d3 are clobbered just afterwards so we don't really need the values there, I figured that I could write

Code:

     move.l     (127*4,a0),d0
     sub.l (126*4,a0),d0

But the moveq is very quick and now I have 16 bit offsets instead of registers (but the *4 operation is done at compile time)

Is my optimisation useful?

Or I could use another register:

Code:

   lea 127*4(a0),a1
   move.l  (A1),d0
   sub.l    -(A1),d0  # pre-decrementing to get offset 126*4

25 May 2022, 16:39	#207
jotd This cat is no more Join Date: Dec 2004 Location: FRANCE Age: 52 Posts: 8,303	Question: I have this '020 code Code: moveq.l #127,d5 moveq.l #126,d3 move.l (a0,d5.l4),d0 sub.l (a0,d3.l4),d0 as d5 and d3 are clobbered just afterwards so we don't really need the values there, I figured that I could write Code: move.l (1274,a0),d0 sub.l (1264,a0),d0 But the moveq is very quick and now I have 16 bit offsets instead of registers (but the 4 operation is done at compile time) Is my optimisation useful? Or I could use another register: Code: lea 1274(a0),a1 move.l (A1),d0 sub.l -(A1),d0 # pre-decrementing to get offset 1264 Last edited by jotd; 25 May 2022 at 18:52.*