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Mac2004



Joined: 15 Dec 2003
Posts: 313
Mac2004
Hi!

This is my try to optimize string length procedure. I wonder if this could be more optimized by using general 32bit instructions. (Meaning, no mmx, sse or anything like that)

Here's my code

Code:
;*******************************************************************************
;STR_Get_length-      The procedure gets asciiz string length (32bit version).
;
;
; Input:  edx--> String pointer
;
; Output: ecx--> String length excluding terminating null.
;*******************************************************************************

STR_Get_length:

   push edx
    
        xor ecx,ecx                 ;Clear counter.

.get_loop:
       add ecx, 4                      ;Update counter.
        test dword[edx],0x000000ff
      jz .sub4

        test dword[edx],0x0000ff00
  jz .sub3
    
        test dword[edx],0x00ff0000
      jz .sub2

        test dword[edx],0xff000000
  jz  .sub1

       add edx, 4
  jmp .get_loop

.sub4: sub ecx,1                       ;Handle final counter fix up.
.sub3:     sub ecx,1
.sub2: sub ecx,1
.sub1: sub ecx,1

.done:
        pop edx 
     ret                             ;The end of procedure

    


regards,
Mac2004
Post 19 Mar 2009, 15:45
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Tomasz Grysztar
Assembly Artist


Joined: 16 Jun 2003
Posts: 7709
Location: Kraków, Poland
Tomasz Grysztar
You should be aware, that running this on a string put at the end of memory block may cause page fault instead of giving the proper result.
Post 19 Mar 2009, 15:54
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Mac2004



Joined: 15 Dec 2003
Posts: 313
Mac2004
Ok, thanx. This procedure is used only on non paged enviroment (meaning paging disabled.)

Regards
Mac2004
Post 19 Mar 2009, 17:54
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LocoDelAssembly
Your code has a bug


Joined: 06 May 2005
Posts: 4633
Location: Argentina
LocoDelAssembly
http://board.flatassembler.net/topic.php?p=71382#71382

But there are more threads about this matter that doesn't use SIMD but I can't search more now.
Post 19 Mar 2009, 18:33
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Mac2004



Joined: 15 Dec 2003
Posts: 313
Mac2004
LocoDelAssembly: Thanx for the link, I will take look at it.

Regards
Mac2004
Post 20 Mar 2009, 03:18
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