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Computer Animation Forum · The Demo Team Src.

#Assembler: The A-Flag

9 messages in this thread

#851From: Nils PipenbrinckNov 14, 1994 3:56 AM

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

#872From: Geoffrey S. KaneNov 14, 1994 5:39 PM

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?

#900From: Nils PipenbrinckNov 15, 1994 6:18 AM

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>)

#917From: Geoffrey S. KaneNov 15, 1994 1:18 PM

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?

#959From: Nils PipenbrinckNov 16, 1994 5:41 AM

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

#966From: Geoffrey S. KaneNov 16, 1994 10:55 AM

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>.

#1002From: Nils PipenbrinckNov 17, 1994 2:23 AM

Hi Geoffrey, I'll ask Dreaden and will post his message here.. I'm sure it's not only interesting to me. Cheers, Nils

#975From: Erik de Neve [Cambrian]Nov 16, 1994 2:29 PM

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 😉

#1003From: Nils PipenbrinckNov 17, 1994 2:23 AM

Hi Erik, I'll take a look at it.. Thank you. Nils