Do these 2 asm-routines the same?

Honitos · 19 April 2024, 09:22

Hi guys,

when investigating the old blitzbasic2 compiler source, I found these two routines.
I guess they do absolutly the same, except the second one being a bit more "smart". Both routines are used!

What it does it to copy the data from adress in A0 until A1 to a destination pointer that is handled by the routine "writeword".

Do you see any possible difference in the output?

pokecode1:

Code:

.pokecode:   ;a0= start of code, a1=end of code
  MOVE.w (A0)+,D1
  BSR.w writeword
 'loop
    CMPA.l A1,A0
    BCC.w 'done
      MOVE.w (A0)+,D1
      BSR.w writeword
  BRA.w 'loop
 'done
RTS

pokecode2:

Code:

.pokecode2:
  MOVE.w (A0)+,D1
  BSR.w writeword
  CMPA.l A1,A0
  BCS.w pokecode2
RTS

jotd · 19 April 2024, 09:49

no. BTW those routines don't take into account that A1 could be equal or below A0, which is a big problem as zero byte memory range would still do something.

Honitos · 19 April 2024, 10:23

Thanks jotd,

I - respectively the original coder - was aware of this and refrained from checking A1 in that routine for speed reasons, I guess.

Photon · 19 April 2024, 18:39

Well, the code already spends a bsr per read word, which should be costly. The second one is slightly faster.

Minimal change to solve the 0 length issue JOTD points out would be

Code:

.pokecode2:
bra.b .pokecode2check
.pokecode2L:
  MOVE.w (A0)+,D1
  BSR.w writeword
.pokecode2check:
  CMPA.l A1,A0
  BCS.w pokecode2L
RTS

Rob68K · 19 April 2024, 20:13

I don't think I've ever used BCC BCS on 68000.
Tell me why I'm wrong.

a/b · 19 April 2024, 20:39

I prefer BHS/BLO aliases unless I'm explicitely checking the C flag (rarely). I find them more self-explanatory (= fewer comments needed), but it also requires more discipline because if you happen to switch to signed, in some cases it's not as trivial as HS/LO -> GE/LT because of the V flag that is part of the signed combo.

19 April 2024, 09:22	#1
Honitos Registered User Join Date: Nov 2019 Location: Celle / Germany Posts: 145	Do these 2 asm-routines do exactly the same thing? Hi guys, when investigating the old blitzbasic2 compiler source, I found these two routines. I guess they do absolutly the same, except the second one being a bit more "smart". Both routines are used! What it does it to copy the data from adress in A0 until A1 to a destination pointer that is handled by the routine "writeword". Do you see any possible difference in the output? pokecode1: Code: .pokecode: ;a0= start of code, a1=end of code MOVE.w (A0)+,D1 BSR.w writeword 'loop CMPA.l A1,A0 BCC.w 'done MOVE.w (A0)+,D1 BSR.w writeword BRA.w 'loop 'done RTS pokecode2: Code: .pokecode2: MOVE.w (A0)+,D1 BSR.w writeword CMPA.l A1,A0 BCS.w pokecode2 RTS Last edited by Honitos; 19 April 2024 at 22:42.

19 April 2024, 18:39	#4
Photon Moderator Join Date: Nov 2004 Location: Eksjö / Sweden Posts: 5,604	Well, the code already spends a bsr per read word, which should be costly. The second one is slightly faster. Minimal change to solve the 0 length issue JOTD points out would be Code: .pokecode2: bra.b .pokecode2check .pokecode2L: MOVE.w (A0)+,D1 BSR.w writeword .pokecode2check: CMPA.l A1,A0 BCS.w pokecode2L RTS

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19 April 2024, 09:49	#2
jotd This cat is no more Join Date: Dec 2004 Location: FRANCE Age: 52 Posts: 8,196	no. BTW those routines don't take into account that A1 could be equal or below A0, which is a big problem as zero byte memory range would still do something.

19 April 2024, 10:23	#3
Honitos Registered User Join Date: Nov 2019 Location: Celle / Germany Posts: 145	Thanks jotd, I - respectively the original coder - was aware of this and refrained from checking A1 in that routine for speed reasons, I guess.

19 April 2024, 20:13	#5
Rob68K Registered User Join Date: Apr 2021 Location: Kingston / UK Posts: 102	I don't think I've ever used BCC BCS on 68000. Tell me why I'm wrong.

19 April 2024, 20:39	#6
a/b Registered User Join Date: Jun 2016 Location: europe Posts: 1,039	I prefer BHS/BLO aliases unless I'm explicitely checking the C flag (rarely). I find them more self-explanatory (= fewer comments needed), but it also requires more discipline because if you happen to switch to signed, in some cases it's not as trivial as HS/LO -> GE/LT because of the V flag that is part of the signed combo.

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