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programming / comp.lang.asm.x86 / Re: PLEASE EXCUSE. I WAS RUDE.

SubjectAuthor
* test al,al setting of ZFbilsch01
+* Re: test al,al setting of ZFRod Pemberton
|+* Re: test al,al setting of ZFKerr-Mudd,John
||`* Re: test al,al setting of ZFTerje Mathisen
|| `* Re: test al,al setting of ZFKerr-Mudd,John
||  `- Re: test al,al setting of ZFKerr-Mudd,John
|`* Re: test al,al setting of ZFbilsch01
| +* PLEASE EXCUSE. I WAS RUDE.bilsch01
| |`- Re: PLEASE EXCUSE. I WAS RUDE.Frank Kotler
| `- Re: test al,al setting of ZFRod Pemberton
`- Re: test al,al setting of ZFBernhard Schornak

1
Subject: test al,al setting of ZF
From: bilsch01
Newsgroups: comp.lang.asm.x86
Organization: A noiseless patient Spider
Date: Tue, 29 Dec 2020 10:26 UTC
Path: i2pn2.org!i2pn.org!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: fy2...@nospicedham.always.com (bilsch01)
Newsgroups: comp.lang.asm.x86
Subject: test al,al setting of ZF
Date: Tue, 29 Dec 2020 02:26:42 -0800
Organization: A noiseless patient Spider
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True or False:
test al,al sets ZF only if al = 0

TIA.   Bill S.



Subject: Re: test al,al setting of ZF
From: Rod Pemberton
Newsgroups: comp.lang.asm.x86
Organization: Aioe.org NNTP Server
Date: Wed, 30 Dec 2020 10:18 UTC
References: 1
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From: nomaili...@nospicedham.trgzxcqvbe.cpm (Rod Pemberton)
Newsgroups: comp.lang.asm.x86
Subject: Re: test al,al setting of ZF
Date: Wed, 30 Dec 2020 05:18:28 -0500
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On Tue, 29 Dec 2020 02:26:42 -0800
bilsch01 <fy247@nospicedham.always.com> wrote:

True or False:
test al,al sets ZF only if al = 0


Look up TEST instruction here:

http://qcd.phys.cmu.edu/QCDcluster/intel/vtune/reference/About_IA-32_Instructions.htm

That's a browse-able HTML version of an IA-32 manual.

--
Sigh ...



Subject: Re: test al,al setting of ZF
From: Kerr-Mudd,John
Newsgroups: comp.lang.asm.x86
Organization: dis
Date: Wed, 30 Dec 2020 12:46 UTC
References: 1 2
Path: i2pn2.org!i2pn.org!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: notsay...@nospicedham.127.0.0.1 (Kerr-Mudd,John)
Newsgroups: comp.lang.asm.x86
Subject: Re: test al,al setting of ZF
Date: Wed, 30 Dec 2020 12:46:50 -0000 (UTC)
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On Wed, 30 Dec 2020 10:18:28 GMT, Rod Pemberton
<nomailings@nospicedham.trgzxcqvbe.cpm> wrote:

On Tue, 29 Dec 2020 02:26:42 -0800
bilsch01 <fy247@nospicedham.always.com> wrote:

True or False:
test al,al sets ZF only if al = 0


Look up TEST instruction here:

http://qcd.phys.cmu.edu/QCDcluster/intel/vtune/reference/About_IA-32_In
structions.htm

That's a browse-able HTML version of an IA-32 manual.

or elsewhere
https://reverseengineering.stackexchange.com/questions/25188/what-does-
test-al-al-mean

Yes. But why do that if you want to test if al=0? far clearer to code
"cmp al,0"

but is cy set identically? back at the OP!

--
Bah, and indeed, Humbug.



Subject: Re: test al,al setting of ZF
From: Bernhard Schornak
Newsgroups: comp.lang.asm.x86
Organization: A noiseless patient Spider
Date: Wed, 30 Dec 2020 13:45 UTC
References: 1
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From: schor...@nospicedham.web.de (Bernhard Schornak)
Newsgroups: comp.lang.asm.x86
Subject: Re: test al,al setting of ZF
Date: Wed, 30 Dec 2020 14:45:22 +0100
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bilsch01 wrote:


True or False:
test al,al sets ZF only if al = 0

TIA.   Bill S.


testb %al, %al

internally performs

andb  %al, %al

without writing the result to the destination. Hence,

andb  %al, %al

sets ZF if %al is zero. in all other cases, ZF is cleared. PF and
SF are set according to %al's content. CF and OF are set to zero,
no matter, what %al currently holds.

"AMD64 Architecture Programmer’s Manual Volume 3: General-Purpose
and System Instructions" [PDF 24594, page 342]


Greetings from Augburg

Bernhard Schornak



Subject: Re: test al,al setting of ZF
From: Terje Mathisen
Newsgroups: comp.lang.asm.x86
Organization: Aioe.org NNTP Server
Date: Wed, 30 Dec 2020 18:12 UTC
References: 1 2 3
Path: i2pn2.org!i2pn.org!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: terje.ma...@nospicedham.tmsw.no (Terje Mathisen)
Newsgroups: comp.lang.asm.x86
Subject: Re: test al,al setting of ZF
Date: Wed, 30 Dec 2020 19:12:37 +0100
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Kerr-Mudd,John wrote:
On Wed, 30 Dec 2020 10:18:28 GMT, Rod Pemberton
<nomailings@nospicedham.trgzxcqvbe.cpm> wrote:

On Tue, 29 Dec 2020 02:26:42 -0800
bilsch01 <fy247@nospicedham.always.com> wrote:

True or False:
test al,al sets ZF only if al = 0


Look up TEST instruction here:

http://qcd.phys.cmu.edu/QCDcluster/intel/vtune/reference/About_IA-32_In
structions.htm

That's a browse-able HTML version of an IA-32 manual.

or elsewhere
https://reverseengineering.stackexchange.com/questions/25188/what-does-
test-al-al-mean

Yes. But why do that if you want to test if al=0? far clearer to code
"cmp al,0"

but is cy set identically? back at the OP!

CMP AX,0 is longer than TEST AX,AX but I'm not sure if the same is true for CMP AL,0? I.e. is there a one-byte form of CMP AL with a one-byte immediate?

Terje

--
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"



Subject: Re: test al,al setting of ZF
From: bilsch01
Newsgroups: comp.lang.asm.x86
Organization: A noiseless patient Spider
Date: Wed, 30 Dec 2020 18:46 UTC
References: 1 2
Path: i2pn2.org!i2pn.org!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: fy2...@nospicedham.always.com (bilsch01)
Newsgroups: comp.lang.asm.x86
Subject: Re: test al,al setting of ZF
Date: Wed, 30 Dec 2020 10:46:46 -0800
Organization: A noiseless patient Spider
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On 12/30/20 2:18 AM, Rod Pemberton wrote:
On Tue, 29 Dec 2020 02:26:42 -0800
bilsch01 <fy247@nospicedham.always.com> wrote:

True or False:
test al,al sets ZF only if al = 0


Look up TEST instruction here:

http://qcd.phys.cmu.edu/QCDcluster/intel/vtune/reference/About_IA-32_Instructions.htm

That's a browse-able HTML version of an IA-32 manual.


I've been using this one.

http://www.felixcloutier.com/x86/

I couldn't believe what I read.
The ref you provide is no more help to me.

I found the following, which I recognize - answered my question.

00000102  BEC87D            mov si,0x7dc8  ;msg: Error.
00000105  AC                lodsb
00000106  84C0              test al,al
00000108  74FC              jz 0x106
0000010A  B40E              mov ah,0xe
0000010C  B307              mov bl,0x7
0000010E  CD10              int 0x10
00000110  EBF3              jmp short 0x105

Consider this: Why not just answer the question that was asked?



Subject: Re: test al,al setting of ZF
From: Kerr-Mudd,John
Newsgroups: comp.lang.asm.x86
Organization: dis
Date: Wed, 30 Dec 2020 19:58 UTC
References: 1 2 3 4
Path: i2pn2.org!i2pn.org!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: notsay...@nospicedham.127.0.0.1 (Kerr-Mudd,John)
Newsgroups: comp.lang.asm.x86
Subject: Re: test al,al setting of ZF
Date: Wed, 30 Dec 2020 19:58:19 -0000 (UTC)
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On Wed, 30 Dec 2020 18:12:37 GMT, Terje Mathisen
<terje.mathisen@nospicedham.tmsw.no> wrote:

Kerr-Mudd,John wrote:
On Wed, 30 Dec 2020 10:18:28 GMT, Rod Pemberton
<nomailings@nospicedham.trgzxcqvbe.cpm> wrote:

On Tue, 29 Dec 2020 02:26:42 -0800
bilsch01 <fy247@nospicedham.always.com> wrote:

True or False:
test al,al sets ZF only if al = 0


Look up TEST instruction here:

http://qcd.phys.cmu.edu/QCDcluster/intel/vtune/reference/About_IA-32
_In
structions.htm

That's a browse-able HTML version of an IA-32 manual.

or elsewhere
https://reverseengineering.stackexchange.com/questions/25188/what-
does-
test-al-al-mean

Yes. But why do that if you want to test if al=0? far clearer to code
"cmp al,0"

but is cy set identically? back at the OP!

CMP AX,0 is longer than TEST AX,AX but I'm not sure if the same is true
for CMP AL,0? I.e. is there a one-byte form of CMP AL with a one-byte
immediate?

Terje

Hugi tips & tricks snippet:


 1. Test the value in AL

 To test whether AL is 0 or 1, one single-byte instruction is enough:

        aaa
        jz      @zero


I'm not claiming it's faster than "test".

--
Bah, and indeed, Humbug.



Subject: PLEASE EXCUSE. I WAS RUDE.
From: bilsch01
Newsgroups: comp.lang.asm.x86
Organization: A noiseless patient Spider
Date: Wed, 30 Dec 2020 20:59 UTC
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From: fy2...@nospicedham.always.com (bilsch01)
Newsgroups: comp.lang.asm.x86
Subject: PLEASE EXCUSE. I WAS RUDE.
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On 12/30/20 10:46 AM, bilsch01 wrote:
On 12/30/20 2:18 AM, Rod Pemberton wrote:
On Tue, 29 Dec 2020 02:26:42 -0800
bilsch01 <fy247@nospicedham.always.com> wrote:

True or False:
test al,al sets ZF only if al = 0


Look up TEST instruction here:

http://qcd.phys.cmu.edu/QCDcluster/intel/vtune/reference/About_IA-32_Instructions.htm That's a browse-able HTML version of an IA-32 manual.


I've been using this one.

http://www.felixcloutier.com/x86/

I couldn't believe what I read.
The ref you provide is no more help to me.

I found the following, which I recognize - answered my question.

00000102  BEC87D            mov si,0x7dc8  ;msg: Error.
00000105  AC                lodsb
00000106  84C0              test al,al
00000108  74FC              jz 0x106
0000010A  B40E              mov ah,0xe
0000010C  B307              mov bl,0x7
0000010E  CD10              int 0x10
00000110  EBF3              jmp short 0x105

Consider this: Why not just answer the question that was asked?


Thanks for your post.   Bill S.



Subject: Re: PLEASE EXCUSE. I WAS RUDE.
From: Frank Kotler
Newsgroups: comp.lang.asm.x86
Organization: Aioe.org NNTP Server
Date: Wed, 30 Dec 2020 23:39 UTC
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From: fbkot...@nospicedham.myfairpoint.net (Frank Kotler)
Newsgroups: comp.lang.asm.x86
Subject: Re: PLEASE EXCUSE. I WAS RUDE.
Date: Wed, 30 Dec 2020 18:39:51 -0500
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On 12/30/2020 03:59 PM, bilsch01 wrote:

....
Thanks for your post.   Bill S.

That's more like it!

Thanks for your question and welcome to clax86.

Best,
Frank
[moderator]




Subject: Re: test al,al setting of ZF
From: Rod Pemberton
Newsgroups: comp.lang.asm.x86
Organization: Aioe.org NNTP Server
Date: Thu, 31 Dec 2020 09:10 UTC
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From: nomaili...@nospicedham.trgzxcqvbe.cpm (Rod Pemberton)
Newsgroups: comp.lang.asm.x86
Subject: Re: test al,al setting of ZF
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On Wed, 30 Dec 2020 10:46:46 -0800
bilsch01 <fy247@nospicedham.always.com> wrote:

The ref you provide is no more help to me.

So, you didn't like the RTFM with a link to the actual manual? ...

Consider this: Why not just answer the question that was asked?

Consider this: What would you learn from any of us simply giving you
the answer? ...

If you didn't understand the explanation in the manual, you could have
easily written some x86 code to test all 256 values for AL.

--



Subject: Re: test al,al setting of ZF
From: Kerr-Mudd,John
Newsgroups: comp.lang.asm.x86
Organization: dis
Date: Thu, 31 Dec 2020 11:30 UTC
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From: notsay...@nospicedham.127.0.0.1 (Kerr-Mudd,John)
Newsgroups: comp.lang.asm.x86
Subject: Re: test al,al setting of ZF
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On Wed, 30 Dec 2020 19:58:19 GMT, "Kerr-Mudd,John"
<notsaying@nospicedham.127.0.0.1> wrote:

On Wed, 30 Dec 2020 18:12:37 GMT, Terje Mathisen
<terje.mathisen@nospicedham.tmsw.no> wrote:

[]

for CMP AL,0? I.e. is there a one-byte form of CMP AL with a one-byte
immediate?

Terje

Hugi tips & tricks snippet:


 1. Test the value in AL

 To test whether AL is 0 or 1, one single-byte instruction is enough:

        aaa
        jz      @zero


I'm not claiming it's faster than "test".


Oops; also jumps if AL is 0x0A



--
Bah, and indeed, Humbug.



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