Posted: Fri Nov 02, 2007 12:25 pm
One misstake i see a lot, is using cx for loops etc, in Pmode.
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Dumbest mistake you have ever made
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Posted: Fri Nov 02, 2007 11:22 pm
Yesterday, i realized that i was setting my esp0 to the current kernel stack not the top of the kernel stack every time I switched a task.
Posted: Sat Nov 03, 2007 6:54 pm
This is why we either use constants and/or use hex.XCHG wrote:I was just writing my file system's driver, and I was wondering why the result of a string comparison on two strings was being inaccurate. Seems that I had put 266 instead of 256 in my code like this:
Code: Select all
LEA EAX , [EDI + 256] LEA EDX , [EBP - (266 + (3*4))]
I have to ENLARGE MY EDITOR'S FONT SIZE
Posted: Sat Nov 03, 2007 7:06 pm
I may be stupid, but I can't see any problem with using cx(c = count) for loops. The only thing I can see is overflow, but then you got to think that there has to be a better way if you have to loop > 65535 times.Dex wrote:One misstake i see a lot, is using cx for loops etc, in Pmode.
EDIT: Also with a bit of trickery, you can extend this to any thing (as along as your stack is big enough).
Posted: Sun Nov 04, 2007 9:52 am
cx is specifically meant for loops...
i think what he meant was using CX instead of ECX -- although it really doesnt matter -- you need an override or two, instead of doubling your data requirement -- it can actually be more efficient to do so...
i think what he meant was using CX instead of ECX -- although it really doesnt matter -- you need an override or two, instead of doubling your data requirement -- it can actually be more efficient to do so...
Posted: Sun Nov 04, 2007 1:40 pm
I meant you should always use ecx for loops in pmode, as it makes a big difference, example:JAAman wrote:cx is specifically meant for loops...
i think what he meant was using CX instead of ECX -- although it really doesnt matter -- you need an override or two, instead of doubling your data requirement -- it can actually be more efficient to do so...
Code: Select all
mov ecx,0x100000
;some code
mov edi,buffer1
mov esi,buffer2
mov cx,4
@@:
movsd
loop @b
;some code
buffer1: times 4 dd 0
buffer2: times 4 dd 0
Posted: Sun Nov 04, 2007 2:15 pm
It's because cx is the lower 2 bytes of ecx, which you're using as a variable. If you were to zero out ecx and not use it as a variable, you'd be set, even while setting only cx.Dex wrote:I meant you should always use ecx for loops in pmode, as it makes a big difference, example:JAAman wrote:cx is specifically meant for loops...
i think what he meant was using CX instead of ECX -- although it really doesnt matter -- you need an override or two, instead of doubling your data requirement -- it can actually be more efficient to do so...Now hands up all though's who think it will only loop 4 times, because you would be wrong.Code: Select all
mov ecx,0x100000 ;some code mov edi,buffer1 mov esi,buffer2 mov cx,4 @@: movsd loop @b ;some code buffer1: times 4 dd 0 buffer2: times 4 dd 0
Posted: Sun Nov 04, 2007 2:44 pm
In ASM you only have a small number of regs to play with, ECX, is one of the general-purpose regs, so has a good chance of being used as such, + if you have to zero ecx, why not just use ECX.
It would also save you a byte .
It would also save you a byte
.Posted: Sun Nov 04, 2007 3:06 pm
actually, I think you should say in x86 ASM...Dex wrote:In ASM you only have a small number of regs to play with, ECX, is one of the general-purpose regs, so has a good chance of being used as such, + if you have to zero ecx, why not just use ECX.
It would also save you a byte
Posted: Sun Nov 04, 2007 5:01 pm
I didn't say using cx was a good idea.Dex wrote:In ASM you only have a small number of regs to play with, ECX, is one of the general-purpose regs, so has a good chance of being used as such, + if you have to zero ecx, why not just use ECX.
It would also save you a byte
'Just pointing out that it doesn't always prove itself to error.Posted: Mon Nov 05, 2007 12:21 pm
you mean you cant use a16? first time i ever heard that, and there is no mention of it in the manuals...
i wonder why...
i dont think you are correct about that...
i wonder why...
i dont think you are correct about that...
Posted: Mon Nov 05, 2007 10:08 pm
I make too many to count. It's a good thing my boss doesn't look over my shoulder while I program. It's hard to describe my dumbest mistakes. My favorite is scratching my head for an hour wondering why my change isn't working: Run the build script stupid! My least favorite is learning Java. My worst mistake is not catching my mistake relying on a coworker to catch it (and fix it).
My worst mistake is not catching my mistake relying on a coworker to catch it (and fix it).Posted: Tue Nov 06, 2007 12:03 am
No body knows your code better than you do.. Unless it's 5 years later and ever you don't understand your own code!babernat wrote:I make too many to count. It's a good thing my boss doesn't look over my shoulder while I program. It's hard to describe my dumbest mistakes. My favorite is scratching my head for an hour wondering why my change isn't working: Run the build script stupid! My least favorite is learning Java.
Posted: Tue Nov 06, 2007 12:06 am
The figure is more like 3 weeks for most people.MessiahAndrw wrote:No body knows your code better than you do.. Unless it's 5 years later and ever you don't understand your own code!
Posted: Tue Nov 06, 2007 7:51 am
At which correctness can look like mistake to the other programmer and you. The best example is another programmer calls you over suspecting you had worked this feature and then grilling you like you had committed the code yesterday. My answer always is something to the effect of, "I cannot tell you the deep magic of the code, you must search for the meaning yourself because in the journey lies the answer." Then I let out an evil laugh and run away.Candy wrote:
The figure is more like 3 weeks for most people.