How to search advanced info when i only get basics?

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l4m2

Joined: 15 Jan 2015
Posts: 674

l4m2 21 Aug 2016, 01:45

I just make an easier-understood example though maybe not true.
Iwant to have the absolute value of eax and I search for it. And I get lots of information saying I should use

Code:

test eax, eax
jns  @f
neg  eax
@@:

but what I want is

Code:

cdq
xor  eax, edx
sub  eax, edx

____________________________
ps. i just want to know how to search advanced info when i only get basics, not trying to get |eax|

21 Aug 2016, 01:45

El Tangas

Joined: 11 Oct 2003
Posts: 120
Location: Sunset Empire

El Tangas 03 Sep 2016, 19:09

Well, searching is an art... for your example, I tried in google:

x86 assembly optimized algorithm absolute value

and easily found the optimized version you gave as example. Even found this equivalent alternative:

Code:

cdq
add eax, edx
xor eax, edx

But this is a simple example...
Other useful keywords:
branchless
parallel
SIMD

03 Sep 2016, 19:09

l4m2

Joined: 15 Jan 2015
Posts: 674

l4m2 14 Sep 2016, 15:59

El Tangas wrote:

Well, searching is an art... for your example, I tried in google:

x86 assembly optimized algorithm absolute value

and easily found the optimized version you gave as example. Even found this equivalent alternative:
Code:
cdq
add eax, edx
xor eax, edx    
But this is a simple example...
Other useful keywords:
branchless
parallel
SIMD

It's just an example for understand, so it's not a good idea to test it (Even if I search for "x86 absolute value" directly some result fits). java random low level didn't give me anything about how it goes

14 Sep 2016, 15:59

El Tangas

Joined: 11 Oct 2003
Posts: 120
Location: Sunset Empire

El Tangas 15 Sep 2016, 16:08

java? You mean you want to program in java bytecode?

15 Sep 2016, 16:08

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