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jotd · 10 November 2021, 21:41

status flags are useful to save cycles. Careful with to-memory operations, as they don't set the status flags. Operations to data registers (not address) do set the status flags.

bclr #0,d0 also sets D0 value before bit is cleared. Can be useful at times. In doubt: RTFM

note: in C, x ^= 1; (in-place xclusive or) is probably faster that x = 1 - x; but optimizers can detect such patterns and change the expression to the fastest one.

@mcgeezer your snippet has issues

Code:

  addq.l #1,FRAME_COUNTER

  move.l FRAME_COUNTER,d0  ; no  "#" there!!!
  and.l #1,d0

although I'd preload the counter value in D0 to save cycles, in this case

Code:

  move.l FRAME_COUNTER,d0
  addq.l #1,d0
  move.l  D0,FRAME_COUNTER
  and.b #1,d0

and and.b does the same there you only need byte value of D0 for the rest of your code probably, instruction fetch is faster (4 bytes instead of 6) although btst #0,d0 probably beats both in terms of speed unless you need the masked value.

10 November 2021, 21:41	#5
jotd This cat is no more Join Date: Dec 2004 Location: FRANCE Age: 52 Posts: 8,303	status flags are useful to save cycles. Careful with to-memory operations, as they don't set the status flags. Operations to data registers (not address) do set the status flags. bclr #0,d0 also sets D0 value before bit is cleared. Can be useful at times. In doubt: RTFM note: in C, x ^= 1; (in-place xclusive or) is probably faster that x = 1 - x; but optimizers can detect such patterns and change the expression to the fastest one. @mcgeezer your snippet has issues Code: addq.l #1,FRAME_COUNTER move.l FRAME_COUNTER,d0 ; no "#" there!!! and.l #1,d0 although I'd preload the counter value in D0 to save cycles, in this case Code: move.l FRAME_COUNTER,d0 addq.l #1,d0 move.l D0,FRAME_COUNTER and.b #1,d0 and and.b does the same there you only need byte value of D0 for the rest of your code probably, instruction fetch is faster (4 bytes instead of 6) although btst #0,d0 probably beats both in terms of speed unless you need the masked value. Last edited by jotd; 10 November 2021 at 21:50.