ASM Community

I have written a test program in asm(masm) and in c++(ms visual c++ 6.0), as following:
in c++ ??

int i, j, k, l

l = 0;
for(i = 0; i < 1000; i++ ) {
for(j = 0; j < 1000; j++ ) {
for( k = 0; k < 1000; k++ ) {
l++;
}
}
}

in asm:
LOCAL i
LOCAL j
LOCAL k
LOCAL l

mov l, 0
mov i, 0
.while i < 1000
mov j, 0
.while j < 1000
mov k, 0
.while k < 1000
inc l
inc k
.endw
inc j
.endw
inc i
.endw

then i compile and run them. I find that the c++ code is fast than the asm code!!!

so why we use asm?

Simple loops are not enough to compare two languages. You must also be aware of that asm itself isn't even faster than Visual Basic, it totally depends on how skilled the person is who writes the code.

Firstly I think the quality of the asm code that you coded is poor. :/ If you are making use of asm, better make use of registers. What is the point of have 8 general purpose registers but not using them? And perhaps you can try replacing the inc with add (According to intel P4 manual, it would be faster). ;)

If you use the C++ code like that, it will produce no code at all since you don't use l (so there's no point in calculating it). If you want it to generate code you need to do something with l after the loop, like returning it from main()..
For example:

int foo()

{

    int l = 0;

    for(int i = 0; i < 1000; i++ ) 

        for(int j = 0; j < 1000; j++ ) 

            for(int k = 0; k < 1000; k++ ) 

                l++;

    return l;

}



int main()

{

    return foo();

}

This is what VC 7.1 outputs as main()

mov    eax, 3B9ACA00h 

ret  

:grin:

Thomas

Isn't 3B9ACA00h = 1000^3? I think it is one of the coolest optimisation I have seen. :stupid:

devilsclaw,
The intel manual states that it is better to replace inc and dec with add and sub as inc and dec only affects a subset of the EFLAG, eg it does not affect carry flag. "This creates a dependence on all previous writes of the flag register." But of course the good thing about inc/dec is that it is one byte short.

There's also another little reason - compilation time :)
I got used to compiling large proggies in asm , for just 1 to 3 seconds.
A week ago I had to install VC++6.0 again, for a job . So, there was a 1000-line code that I had to compile to see how the plugin works, and :eek: 50 seconds. Of course, I can later make a "precompiled header" and incremental compiling, but the first shock stays. Good that it isn't as slow as VB - a 500-line code had to compile for 15 minutes :eek: :eek:
I love testing my code incrementally - this way there are no bugs left, and even a 3-second difference in compilation time is critical for such an operation. (I guess :grin: )

this discussion has been taking place over and over :( , don't you think?
Use the search, Luke! :)

The 'pure' code generated by a compiler won't really be that much larger than similar code in assembly (with the same amount and type of optimizations applied). Sure, you have some hits because of the runtime libraries included, but how bad is 75k if your application is 500k large? Besides, you should really use the runtime functions, so that there will be very little dead code.

And if you want to do "to the bones" API programming without the runtime library, well, just about every C/C++ compiler (and a lot of other HLLs) will let you not link in the runtimes, and then your executable size can compete with assembly.

If you just apply a little care and consideration while designing and programming, you can get nice results... whether you use a highlevel language or not. Iirc, farbrausch's FR-08 64k winning intro at The Party 2000 was coded in C++.

Actually, I once saw GCC (with -O3) replace a function call (passed a constant parameter), that called another function, that computed some value based on the original parameter, with a single MOV instruction. Now *that* was quite impressive. Of course, it took forever to compile and the "-O3" setting isn't safe for all programs, but it was still *very* impressive.
Cheers,
Randy Hyde

_Shawn, in fact, yes. I had to use a 233MHz - 32ram Pc, that was burdened as a server for other 10 PCs , and maybe the code was more than 500 (maybe 5000), but I remember how much I was sweating, waiting for this compilation to complete, in front of my employer. I had to fix some program , and create my own installation, that would install the files on even the worst PC one could find these days. I managed to complete the job, "ULIS" is the installation package I posted here. Then I was asked to make a VB database program, whose development the employer and my colleagues dragged down, and finally didn't pay me anything for either of the tasks. :stupid:
My PC at home isn't good for computation either. But my GPU is cool - GeForce2, so I can still play some games.
but at least I can play mp3 :), and my own musical software :)

In a related item, see my new post in this thread:

http://www.asmcommunity.net/board/index.php?topic=15286

:grin: