Programming Forums - String reversal

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- - String reversal (http://www.programmingforums.org/showthread.php?t=5982)

I didn't want to keep polluting Jim's thread with non-C code, so the saga continues...

This algorithm is more robust and runs in 49-53 cycles on my P4. Comments, critiques, and corrections always welcome.

I'll be out of town for a couple of days since someone here gave my wife the bright idea of gettin' away from my routine. I won't mention any names but their initials are INFINITE RECURSION and TEECHA!!! She's even making me drive! Next thing you know she'll be making me sleep in a tent, or a cave! :D

DaWei, don't be booby trappin' my house while I'm gone. :p

;Reverse a string



str1 db 'abcdefghijklmnopqrstuvwxyzabc',0

str2 db 64 dup(0)



        lea esi,str1                        

        lea edi,str2

        mov ecx,[sizeof str1-2]

        cmp ecx,7

        ja l0

        or ecx,ecx

        jnz @f

        mov al,[esi]

        mov [edi],al

        add edi,1

        jmp l3

        

@@:     mov al,[esi+ecx]

        mov [edi],al

        add edi,1

        sub ecx,1

        jnz @b

        mov al,[esi]

        mov [edi],al

        add edi,1

        jmp l3



l0:     mov ebx,ecx

        shr ecx,2

        shl ecx,2

        sub ebx,ecx

        jz l1

        cmp ebx,3

        jnz @f

        mov al,[esi+ecx+3]

        sub ebx,1

        mov [edi],al

        add edi,1



@@:        cmp ebx,2

        jnz @f

        mov al,[esi+ecx+2]

        sub ebx,1

        mov [edi],al

        add edi,1



@@:        cmp ebx,1

        jnz l1

        mov al,[esi+ecx+1]

        mov [edi],al

        add edi,1

        

l1:     mov al,[esi+ecx]

        mov [edi],al

        add edi,1



l2:     sub ecx,4

        mov eax,[esi+ecx]         ; 4 byte aligned string now

        bswap eax

        mov [edi],eax

        add edi,4

        or ecx,ecx

        jnz l2                           

l3:

@lostcauz: you must have been really bored :D.. nice code ;)

lol @ lostcauz... aren't women great :) Have fun man...

Here is where we are staying: http://ozarkcave.com

Women are great!! You men wouldn't know what to do without us!!! =0)

What's wrong with sleeping in a cave, lostcauz? lol

Yes, I agree women are great and I definitely would be lost without her.

We went to a secluded area and I must say it sucked canal water! Now my back hurts, I have a cold, my feet hurt and to top it off I'm covered in poison oak. Thanks a lot! :p I won't be mentioning where you guys decided to go or sure enough I'll be a cave dweller next. :eek:

str1 db 'abcdefghijklmnopqrstuvwxyzabc',0

str2 db 64 dup(0)



        lea esi,str1           ; 43-45 cycles

        lea edi,str2

        mov ecx,[sizeof str1-1]

        mov ebx,ecx

        cmp ecx,4

        jb l1

        and ebx,3           ; test for alignment

        jz l2

        cmp ebx,3

        jnz @f

        sub ecx,1

        mov al,[esi+ecx]

        sub ebx,1

        mov [edi],al

        add edi,1



@@:        cmp ebx,2

        jnz @f

        sub ecx,1

        mov al,[esi+ecx]

        sub ebx,1

        mov [edi],al

        add edi,1



@@:        cmp ebx,1

        jnz l1

        sub ecx,1

        mov al,[esi+ecx]

        mov [edi],al

        add edi,1

        jmp l2

        

l1:        sub ecx,1          ; string is less than 4 characters

        mov al,[esi+ecx]

        mov [edi],al

        add edi,1

        or ecx,ecx

        jz l3

        jmp l1

        

l2:        sub ecx,4

        jnz @f

        mov eax,[esi+ecx]         

        bswap eax

        mov [edi],eax 

        jmp l3

           

@@:        mov eax,[esi+ecx] ; 4 byte aligned string

        bswap eax

        mov [edi],eax

        add edi,4

        sub ecx,4 

        jnz @b                           

        mov eax,[esi]         

        bswap eax

        mov [edi],eax

l3:

See... Now your woman can take care of you and all your ailments! ;)

Quote:

What's wrong with sleeping in a cave, lostcauz? lol

Nothing when it has 6 million dollars worth of technological rennovations, including dehumidifiers and jacuzzis :) LOL

Quote:

I'm covered in poison oak.

lol, ya gotta stop rolling around in the woods man.

Quote:

Now your woman can take care of you and all your ailments!

and if not, just scratch the poision oak spot and offer to give her a massage :)

Dehumidifier... hmmm.. I need one of those in my classroom NOW!! I'm about to sweat to death, and being in a little bitty room with 22 other people doesn't help matters :(

Reading this thread is getting under my skin. Pooh on you. I think I'll wait about a month and take a Caribbean cruise. Noooooo poison oak be's dere. :p