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Offline BuckeyeDude

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Signed Comparison Broked
« on: May 03, 2010, 11:42:48 pm »
Not sure if anyone else has mentioned this, but the signed comparison in Axe doesn't work.
Code: [Select]
-1->A
25->B
If A>>B
Returns true. I did a quick check at your code generation and it seems to me it would be easier to check the high order register first then do a normal compare on the lower, although I dont know if you had other reasons for doing it this way.

I should also add that I was quite impressed with the speed of the parser and code generation. Can't wait to see more in the future.

Offline Quigibo

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Re: Signed Comparison Broked
« Reply #1 on: May 03, 2010, 11:53:56 pm »
Thanks for pointing that out!  Actually, I've already fixed that in the next version.  I've been spending most of this entire week just going through all the math routines and making them more efficent both on the parser side and the code generation.  Also, there were a lot more bugs than I thought (like this one).  I've fixed at least 5 different bugs already, mostly on the parsing side, and it seems to be running much smoother.  I'll be updating in a few hours probobly.

That's a good idea to do seperate high and low comparisons, I'll see if it reduces the size.
« Last Edit: May 03, 2010, 11:54:47 pm by Quigibo »
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Offline DJ Omnimaga

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Re: Signed Comparison Broked
« Reply #2 on: May 03, 2010, 11:56:57 pm »
I never noticed that x.x

I never used signed comparisons so far but later, I might haev ran into that issue if I ever coded something like a RPG x.x

Offline Quigibo

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Re: Signed Comparison Broked
« Reply #3 on: May 04, 2010, 01:06:30 pm »
Well, I couldn't find a way to do it with high and low comparisons separately.  Here is what I'm using now.  I might be able to optimize it using the parity flag, but I'm avoiding absolute jumps at the moment.

Code: [Select]
p_SIntGt:
ex de,hl
xor a
ld b,h
sbc hl,de
ld h,a
rra
xor b
xor d
rlca
and 1
ld l,a
p_SIntGe:
xor a
ld b,h
sbc hl,de
ld h,a
rra
xor b
xor d
rlca
sbc a,a
inc a
ld l,a
p_SIntLt:
xor a
ld b,h
sbc hl,de
ld h,a
rra
xor b
xor d
rlca
and 1
ld l,a
p_SIntLe:
ex de,hl
xor a
ld b,h
sbc hl,de
ld h,a
rra
xor b
xor d
rlca
sbc a,a
inc a
ld l,a

BuckeyeDude, do you have a routine smaller than this?  These are 12 and 13 bytes depending on if they need the exchange.
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Offline Iambian

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Re: Signed Comparison Broked
« Reply #4 on: May 04, 2010, 04:06:34 pm »
I want to see how far you can get with this idea:
Code: [Select]
;76543210
;SZ-H-VNC

ex de,hl
xor a
sbc hl,de
push af
pop hl
ld a,L
rlca
and 1
ld L,a
It relies on the stack and the fact that the sign bit is the 7th flag bit. Not entirely sure if this does anything, since I'm not too experienced in signed stuffs. I'm assuming you represent these numbers as some form of two's compliment. If you can use the idea, feel free to do so.
« Last Edit: May 04, 2010, 04:15:26 pm by Iambian »
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Offline calc84maniac

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Re: Signed Comparison Broked
« Reply #5 on: May 04, 2010, 04:51:30 pm »
The signed comparison result needs to be an XOR of the V and S flags (since if there was an overflow, you have the wrong sign)
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Offline Iambian

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Re: Signed Comparison Broked
« Reply #6 on: May 04, 2010, 05:11:26 pm »
Nevermind then. My approach wouldn't save anything...
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