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Index > Main > The most useless instruction

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Teehee



Joined: 05 Aug 2009
Posts: 570
Location: Brazil
Teehee 19 Jun 2011, 17:56
LOOP ?

everybody say it is slow and should be replaced by Jcc instr. ..

Which others instructions are "useless"?

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Post 19 Jun 2011, 17:56
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ouadji



Joined: 24 Dec 2008
Posts: 1081
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ouadji 19 Jun 2011, 20:20

jecxz ?

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Post 19 Jun 2011, 20:20
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edfed



Joined: 20 Feb 2006
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edfed 19 Jun 2011, 20:28
xchg ebp,ebp
Post 19 Jun 2011, 20:28
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typedef



Joined: 25 Jul 2010
Posts: 2909
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typedef 19 Jun 2011, 21:07
ouadji wrote:

jecxz ?


Hmmmm ?

Would you rather

Code:
cmp ecx,0
je    .xxx
    

Post 19 Jun 2011, 21:07
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Teehee



Joined: 05 Aug 2009
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Teehee 19 Jun 2011, 21:51
edfed wrote:
xchg ebp,ebp

not so useless: a 2-bytes NOP Smile

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Post 19 Jun 2011, 21:51
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vid
Verbosity in development


Joined: 05 Sep 2003
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vid 19 Jun 2011, 21:56
Where is tom when we need him? Very Happy
Post 19 Jun 2011, 21:56
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Teehee



Joined: 05 Aug 2009
Posts: 570
Location: Brazil
Teehee 19 Jun 2011, 22:00
typedef wrote:
ouadji wrote:

jecxz ?


Hmmmm ?

Would you rather

Code:
cmp ecx,0
je    .xxx
    



maybe bc the common is

Code:
dec ecx
jz  .xxx    

?
it seems rare a cmp ecx,0 out of a loop.

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Post 19 Jun 2011, 22:00
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ouadji



Joined: 24 Dec 2008
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ouadji 19 Jun 2011, 22:41
Code:
or ecx,ecx
jz mylabel    
I prefer "or/jz" to "jecxz"
with "jecxz" the jump is limited to 128 bytes, in many cases it's not enough.
There should be a "near version" of jecxz !
and it seems that it's faster too! (??)

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Post 19 Jun 2011, 22:41
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Tyler



Joined: 19 Nov 2009
Posts: 1216
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Tyler 20 Jun 2011, 03:33
lea is pretty pointless.
Post 20 Jun 2011, 03:33
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mindcooler



Joined: 01 Dec 2009
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mindcooler 20 Jun 2011, 04:34
jecxz is pretty useless if you use ebx as your counter Razz
Post 20 Jun 2011, 04:34
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idle



Joined: 06 Jan 2011
Posts: 410
Location: Ukraine
idle 20 Jun 2011, 11:28
sub eax,eax
cmovnz eax,[eax]
Post 20 Jun 2011, 11:28
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Teehee



Joined: 05 Aug 2009
Posts: 570
Location: Brazil
Teehee 20 Jun 2011, 11:54
Tyler wrote:
lea is pretty pointless.

++++++++++++++1 Razz

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Post 20 Jun 2011, 11:54
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Overflowz



Joined: 03 Sep 2010
Posts: 1046
Overflowz 20 Jun 2011, 12:17
Quote:
lea is pretty pointless.

No way! It' saves alot of work for me :p
Post 20 Jun 2011, 12:17
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edfed



Joined: 20 Feb 2006
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edfed 20 Jun 2011, 12:35
lea is good, it means:

X=Y*scale+Z+Constant

then, it is not so pointless, it is some advanced signal processing instruction.
Post 20 Jun 2011, 12:35
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JohnFound



Joined: 16 Jun 2003
Posts: 3499
Location: Bulgaria
JohnFound 20 Jun 2011, 12:45
"loop" is great instruction for programmers (also string instructions) it is not our fault they are slow. In most cases using "loop" makes your code readable and small.
For example FASM uses "non optimal" instructions all over the source, but it is still, the fastest assembler in the world.
How is it possible? Meditate on this. Smile
Post 20 Jun 2011, 12:45
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
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revolution 20 Jun 2011, 13:46
FFREE

Does anyone actually use it in a beneficial way?
Post 20 Jun 2011, 13:46
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idle



Joined: 06 Jan 2011
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idle 20 Jun 2011, 14:44
fnop - dangerous nop ?
Post 20 Jun 2011, 14:44
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cod3b453



Joined: 25 Aug 2004
Posts: 618
cod3b453 20 Jun 2011, 18:27
I'd go for ud2 Laughing
Post 20 Jun 2011, 18:27
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xleelz



Joined: 12 Mar 2011
Posts: 86
Location: In Google Code Server... waiting for someone to download me
xleelz 21 Jun 2011, 01:43
what is std and cld good for?
Post 21 Jun 2011, 01:43
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 19076
Location: In your JS exploiting you and your system
revolution 21 Jun 2011, 01:55
xleelz wrote:
what is std and cld good for?
Both STD and CLD are good for getting you to visit the doctor.
Post 21 Jun 2011, 01:55
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