RE: code optomization:any way to do this better?

  • From: "Ken Perry" <whistler@xxxxxxxxxxxxx>
  • To: <programmingblind@xxxxxxxxxxxxx>
  • Date: Sun, 16 Jan 2011 22:53:15 -0500

I don't think there is a really good way to speed this up.  The fact is most
assemblers will turn this into some really optimized machine code and with
chips now days they can do multiple look ahead if statements so that this
would almost happen in one pulse of a chips timing. I think Sina might be
able to talk on the speed of this better than I but I can tell you the code
is not bad.  You have to understand  Asm is different than most languages
because its normal to have some repetitive code.  You could make a block
that tests for null and returns you to a passed in location so that way
every time you wanted to test for null you jump to your test block and then
if its null jump to end or jump back to the location in the code where you
wanted to be but I don't see any gain in doing that.

Ken


-----Original Message-----
From: programmingblind-bounce@xxxxxxxxxxxxx
[mailto:programmingblind-bounce@xxxxxxxxxxxxx] On Behalf Of Littlefield,
Tyler
Sent: Sunday, January 16, 2011 9:56 PM
To: programmingblind@xxxxxxxxxxxxx
Subject: code optomization:any way to do this better?

So I've been playing with assembly a lot lately, and was curious if 
there was a better way to do this. most importantly, the whole three 
branched if check (null, not null).
section .text
global _strcmp
_strcmp:
enter 0,0
;we copy our arguments to EBX and ECX
mov EBX, [EBP+8]
mov ECX, [EBP+12]
.loop:
;we need one value in a register
mov EDX, [ECX]
;check for null termination
cmp byte [EBX], 0
je .null
jne .notnull
;we have a null termination.
;if the other string is null terminated, we jump to success. otherwise 
it fails because they obviously aren't equal.
.null:
cmp byte [ECX], 0
je .success
jne .fail
;byte wasn't null, now we check for null on the other byte.
;if one is null, it's a fail because again they aren't equal. If it is 
not null, we do another check.
.notnull:
cmp byte [ECX], 0
;not equal, we check for equalness between the two now.
jne .check
je .fail
;we check for equalness between the two bytes here.
.check:
cmp [EBX], EDX
je .next
jne .fail
;here we increase pointers and jump back up to the top of the loop.
.next:
inc EBX
inc ECX
jmp .loop
;strings compared fully
.success:
mov EAX,1
jmp .finish
;strings did not compare fully.
.fail:
mov EAX, 0
;code cleanup.
;no need for a jmp, it just falls through.
.finish:
leave
ret

-- 

Thanks,
Ty

__________
View the list's information and change your settings at 
//www.freelists.org/list/programmingblind

__________
View the list's information and change your settings at 
//www.freelists.org/list/programmingblind

Other related posts: