#Assembler: The A-Flag
9 messages in this thread
#Assembler: The A-Flag — declared parent_msg_num=(none), resolved parent_id points to #(none)
Hi folks,
I just discovered the A-flag.. but don't have a cpu-reference and don't know
when the A-flag is set or reset.
If you know anything about this mystery flag please reply. Maybe I can speed up
a lot of my algorithms…
SUBMiSSiVE
#851-#Assembler: The A-Flag — declared parent_msg_num=851, resolved parent_id points to #851
Nils,
I won't pretend to be an Asm guru, but…
BTW, my book lists an AF (Auxiliary carry) and a AC (Alignment check enabled)
flag. The AF is bit 4, and AC is bit 18 –NOTE: AC is a '486 only flag.
The AF is affected by: AAA, AAD*, AAM*, AAS, ADC, ADD, AND*, CMP,
CMPSB, CMPSD, CMPSW, CMPXCHG, DAA, DAS, DEC, DIV*, IDIV*, IMUL*, INC,
IRET, MUL*, NEG, OR*, POPF, POPFD, SAHF, SAL*, SAR*, SBB, SCASB,
SCASD, SCASW, SHL*, SHLD*, SHR*, SHRD*, SUB, TEST*, XADD and XOR*.
-NOTE: * means flag-change is "undefined" –that's what my
book says, I'm not sure what that means.
This info is from Tables 17.5 & 17.6 pp 652-3 in "Using
Assembly Language: 2nd Edition" Allen L. Wyatt, QUE: (c) 1990
ISBN 0-88-22-464-9
The AC flac is affected only by IRET.
My book does NOT cover P5 instructions, so I'm not sure about them.
I've double-checked my lists, but I CANNOT guarantee them –USE AT OWN RISK.
If you need a description of any of these instructions, just ask.
Hope this helps,
Jeff
P.S. > SUBMiSSiVE < <–huh?
#872-#Assembler: The A-Flag — declared parent_msg_num=872, resolved parent_id points to #872
Hi Geoffrey,
Thank you.. But when will the A-Flag be set? The C, Z and O-Flags are easy to
use, but what is an Auxilary-Carry?
SUBMiSSiVE (what do you think, when you here this handle <g>)
#900-#Assembler: The A-Flag — declared parent_msg_num=900, resolved parent_id points to #900
Nils,
> Thank you.. But when will the A-Flag be set? The C, Z and O-Flags are easy >
to use, but what is an Auxilary-Carry?
Good question. I'm digging deeper, withiout much luck. My guess is that the
A-Flag is used internally, possibly to help determine what the carry flag
should be –but they (Intel, MicroSloth, etc.) think you don't need to know.
If I find anything I'll let you know, but don't hold your breathe. BTW, what
do you need it for anyway? Just asking.
Jeff
P.S. > SUBMiSSiVE (what do you think, when you here this handle <g>) <
–well, yes some things do come to mind, but it's not something I
would announce. Is there a hidden meaning?
#917-Assembler: The A-Flag — declared parent_msg_num=917, resolved parent_id points to #917
HI Geoffrey,
I'll post my question in the IBM-PRO forum.. There are really
assembler-wizzards. I'm sure they know what the A-Flag is… By the way.. At
the moment I guess that the flag has something to do with nibble or
bcd-arithmetics (maybe a nibble-overrun).
Have a nice day,
SUB
By the way.. Of cause it's a hidden meaning… I thought it was obvious
#959-#Assembler: The A-Flag — declared parent_msg_num=959, resolved parent_id points to #959
Nils,
Good luck on your quest. You might want to e-mail Draeden of VLA. He can be
reached at draeden@u.washington.edu.
Jeff
> By the way.. Of cause it's a hidden meaning… I thought it was obvious
Of course, it's the good old obvious hidden meaning!!! I knew I was missing
something <g>.
#966-Assembler: The A-Flag — declared parent_msg_num=966, resolved parent_id points to #966
Hi Geoffrey,
I'll ask Dreaden and will post his message here.. I'm sure it's not only
interesting to me.
Cheers,
Nils
#851-#Assembler: The A-Flag — declared parent_msg_num=851, resolved parent_id points to #851
Hi Nils,
See my program 'FLAGTEST' on the IBMPRO forum in the assembly library.
It also contains some documentation. (not A-flag specific though)
Cheers, Erik 'Mr. Flag' de Neve 😉
#975-Assembler: The A-Flag — declared parent_msg_num=975, resolved parent_id points to #975
Hi Erik,
I'll take a look at it.. Thank you.
Nils