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The carry flag   Message List  
Reply | Forward Message #13866 of 15019 |
Re: [gbadev] Re: The carry flag


you completely missed my point. i was pointing out the problem with
operating the carry bit in this manner.



----- Original Message -----
From: "Groepaz" <groepaz@...>
To: <gbadev@yahoogroups.com>
Sent: Tuesday, April 01, 2003 3:59 AM
Subject: Re: [gbadev] Re: The carry flag


> On Monday 31 March 2003 22:15, Morten Pedersen wrote:
> > but that's completely retarded. that means (and i just tested this to be
> > true) the following code ends up with '1' in r12.
> >
> > mov r10,#0x00000000
> > mov r11,#0x00000000
> > subs r12,r10,r11
> > adc r12,r10,r11
>
> the last one should be ADD not ADC (which adds the carry => 1) :=)
>
> gpz
>
>
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
Tue Apr 1, 2003 7:17 pm

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escapekey@...
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Forward 		Message #13866 of 15019 |
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... You must mean that SBC was (A + ~B + C) = (A - B - 1 + C) = (A - B - borrow). SUB has to include the 1 adjustment or else its just *wrong* :-) Note also...
Eddie Edwards
eddie@...
Send Email 		Apr 2, 2003
12:01 am

you completely missed my point. i was pointing out the problem with operating the carry bit in this manner. ... From: "Groepaz" <groepaz@...> To:...
Morten Pedersen
escapekey@...
Send Email 		Apr 2, 2003
12:02 am

... well eh :o) i just see no "problem" here at all :o) (or the point where the behaviour is not consistent for that matter). the fact that your calculation ...
Groepaz
groepaz2000
Offline Send Email 		Apr 2, 2003
2:38 am

... You haven't pointed out any problem at all. What *is* the problem with operating the carry bit in this manner? If there's a genuine problem with the ARM...
Eddie Edwards
eddie@...
Send Email 		Apr 2, 2003
5:20 pm

... Can you justify why the carry flag should be set in this case? ... I confirmed that this is does occur (at least in the VisualBoy emulator). This is not...
Jay Dresser
JTGD
Offline Send Email 		Apr 3, 2003
12:16 am

... You're simply labouring under a misunderstanding of how carry flags work. The only thing incorrect here is following SUBS with ADC. There is no meaning to...
Eddie Edwards
eddie@...
Send Email 		Apr 3, 2003
2:16 am

Is there a quick and simple test for detecting the SP version ? over the older GBA? I have a help page screen that lists controls for GBA, and wish to display...
Bollo
bolloxim
Offline Send Email 		Apr 3, 2003
9:35 am

... unfortunately, no. there isn't even a long and complicated test for detecting the SP. it's totally transparent to the programmer. regards, matthew....
matthew conte
whatwouldbig...
Offline Send Email 		Apr 3, 2003
1:28 pm

Hi Bollo, I asked this on the gbadev.org forums, and there was no method known as of yet. I tried dumping the BIOS as well, to see if anything had changed,...
Dennis Munsie
bea_dennis
Offline Send Email 		Apr 3, 2003
7:27 pm

but doesn't final fantasy tactics advance change its colors depending on whether its running on the GBA or the SP? if so, then there must be some way to detect...
Akshay Dhalwala
akdjr
Offline Send Email 		Apr 4, 2003
12:02 am

Doesn't FFTA use a menu to select the color settings? I could've sworn that I had read that someplace. dennis...
Dennis Munsie
bea_dennis
Offline Send Email 		Apr 4, 2003
2:36 am

Metroid Fusion asks you if you are using headphones or internal speaker and changes the sound depending on your selection. Although its nice to autodetect to...
Aaron Isaksen
aisaksen@...
Send Email 		Apr 4, 2003
2:35 am

Hi, You can choose the color settings from the menu. There are even settings for when you're playing through the Gameboy Player for the NGC. Bye, Collin ... ...
Collin van Ginkel
fleppes2001
Offline Send Email 		Apr 4, 2003
8:24 am

... that would also be a reliable way to make sure you are on a gba ;) cheers, x -- chris@... Postmodernism is german romanticism with better ...
CK
x@...
Send Email 		Apr 4, 2003
10:59 am

... OK, I can't reproduce it now with the same conditions as before, so I retract my complaint. If I investigate again, I will confirm on actual hardware. It...
Jay Dresser
JTGD
Offline Send Email 		Apr 3, 2003
9:36 am

Hi Jay, ... Both correct. CMP is *exactly* just SUBS without a destination register. ... <=> BCC. ... Well you should avoid BCC/BCS except (a) after ADD and...
Eddie Edwards
eddie@...
Send Email 		Apr 3, 2003
1:27 pm

... maybe an old speccy owner that still cant resist any 6502-ish behaviour no matter what? :o) gpz...
Groepaz
groepaz2000
Offline Send Email 		Apr 3, 2003
2:17 am

... yes, I was taking about the old 6502 (history of the Arm being the replacement for the 6502 in acorn computers) (still it was sbc without the sub etc etc)....
Mike Wynn
mike.wynn@...
Send Email 		Apr 2, 2003
2:43 am

of course this might very well be purely academic, but the result is still incorrect regardless of how you turn it. ((0-0)+0+(c)) should never result in 1. as...
Morten Pedersen
escapekey@...
Send Email 		Apr 2, 2003
11:36 pm

... Academically, does Peano arithmetic define 'c'? What's incorrect academically is to use the carry flag for anything other than carrying from less...
Damian Yerrick
yerricde
Offline Send Email 		Apr 2, 2003
11:54 pm

... This really perplexed me so I tried it out myself as a sanity check. I was unable to reproduce this behaviour either in VBA or on the hardware. ?!?...
Chris Hayton
you_oughta_b...
Offline Send Email 		Apr 3, 2003
2:16 am

i cant reproduce it either so i probably forgot the s bit or something anyway, cheers all ... From: "Chris Hayton" <chayton@...> To:...
Morten Pedersen
escapekey@...
Send Email 		Apr 3, 2003
9:36 am
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