Thanks for the book. I've seen that before, just thought it was for the high-level assembly instead of... assembly. :) I guess my last question, though not so related to asm is this. I'm able to navigate through the instruction reference (and something tells me that our processors would be so much faster without 500000 instructions), but looking at the optomization manual I have problems because they aren't links, and I have like 3-8 (I assume chapter 3, page 8). Is there a way to navigate by chapter with this mess? I'm able to click links (I just use u, as down arrow has problems reading contents), until I hit after M, where the first volume dead-ends. then I need to look at the page number, control+shift+n in volume 2 and go there. It's a bit off, but a control+page down 1-5 times does the trick. Slowish, but it works I suppose. To bad it's secure, I'd just start ripping all this out and making a nice table with all the pages.
On 1/17/2011 9:32 AM, Sina Bahram wrote:
Also, I'd advise you to take a look at the following Note: all the following examples assume that es and ds are pointing at the proper segments containing the destination and source strings. Comparing Str1 to Str2: lea si, Str1 lea di, Str2 ; Get the minimum length of the two strings. mov al, Str1 mov cl, al cmp al, Str2 jb CmpStrs mov cl, Str2 ; Compare the two strings. CmpStrs: mov ch, 0 cld repe cmpsb jne StrsNotEqual ; If CMPS thinks they're equal, compare their lengths ; just to be sure. cmp al, Str2 StrsNotEqual: At label StrsNotEqual, the flags will contain all the pertinent information about the ranking of these two strings. You can use the conditional jump instructions to test the result of this comparison. Art of assembly: http://webster.cs.ucr.edu/AoA/DOS/ch15/CH15-3.html take care, Sina -----Original Message----- From: programmingblind-bounce@xxxxxxxxxxxxx [mailto:programmingblind-bounce@xxxxxxxxxxxxx] On Behalf Of Littlefield, Tyler Sent: Monday, January 17, 2011 11:06 AM To: programmingblind@xxxxxxxxxxxxx Subject: Re: code optomization:any way to do this better? On a side note, here's my code cleaned up, for anyone who cares. 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 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. je .fail ;we check for equalness between the two bytes here. .check: cmp [EBX], EDX 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. .finish: leave ret On 1/17/2011 9:03 AM, Littlefield, Tyler wrote:OK, a couple questions from your message. I can see letting things fall through, and I actually got rid of a jmp before this. My question is how I should handle this without those paths. For example, I need to check the two strings, to make sure that there is something there, or that one of the bytes is not null. Last, what do you mean by promote the code up one level? Thanks, On 1/17/2011 8:48 AM, Sina Bahram wrote:You have to do the same thing that I suggested in my last mail with your fail and success jumps. Here is a rule. Never, ever, ever, never, ever have two orthogonal jumps beside one another. You will never have a situation where you need more than one jump, because mathematically, this is equivalent to this: If(true) Do stuff Else if(false) Do stuff That's redundant, right? Because of course the else is false, there's no need to check it. Also, you need to promote code up a level, if you'd like less code space bloat. You compare the byte stored at ECX to 0 in both branches of your jump, then you jump based on that result. Get rid of it from both branches. In fact, just get rid of those branches all together. There is no point ot them, since they contain the same code, before they each individually jump to fail, success, notnull, and null, or whatever the heck the four paths are. So just collapse all these jumps down. Take care, Sina -----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
