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www.waraxe.us Forum Index -> Assembler -> mmx strlen implementation
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mmx strlen implementation
PostPosted: Sat Feb 04, 2006 3:19 pm Reply with quote
erg0t
Valuable expert
Valuable expert
 
Joined: Apr 08, 2005
Posts: 55
Location: Uruguay




Hi, yesterday I was iluminated and it ended in a very fast and small strlen implementation. It uses 2 general registers, two mmx registers, and has only one branch. Can be modified easly to scan for another bytes.
Here is the fasm macro:

macro strlen Param
{
mov ecx, Param
pxor mm1,mm1
sub ecx, 8
bucle:
add ecx, 8
movq mm0, [ecx]
pcmpeqb mm0,mm1
pmovmskb eax,mm0
test eax, eax
jz bucle
sub ecx, Param
bsf eax, eax
add eax, ecx
}
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PostPosted: Tue Feb 07, 2006 7:54 pm Reply with quote
erg0t
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Valuable expert
 
Joined: Apr 08, 2005
Posts: 55
Location: Uruguay




I optimized a little the rutine.
Benchmarks:

old
Quote:

real 0m9.412s
user 0m9.355s
sys 0m0.025s

new
Quote:

real 0m8.120s
user 0m8.073s
sys 0m0.019s


new code:
Quote:

macro strlen Param
{
mov ecx, Param
pxor mm1,mm1
bucle:
movq mm0, [ecx]
add ecx, 8
pcmpeqb mm0,mm1
pmovmskb eax,mm0
test eax, eax
jz bucle
bsf eax, eax
lea eax, [ecx+eax-8]
sub eax, Param
}
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PostPosted: Thu Feb 09, 2006 12:00 am Reply with quote
LINUX
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Joined: May 24, 2004
Posts: 404
Location: Caiman




iluminated code Smile

personal note > pone el source del bot aka no seas careta
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PostPosted: Thu Feb 09, 2006 12:05 am Reply with quote
erg0t
Valuable expert
Valuable expert
 
Joined: Apr 08, 2005
Posts: 55
Location: Uruguay




LINUX wrote:
iluminated code Smile

personal note > pone el source del bot aka no seas careta

todavia le falta xD
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mmx strlen implementation
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