Assembly On iPAQ

[Digby]

I've done quite a bit of ARM assembly language programming.  If you have questions that the ARM reference docs can't answer, feel free to ask me.<br><br>

[Phantom]

[Dan East]

[Digby]

[Dan East]

[Zensunni]

[Digby]

[Zensunni]

[Mole]

Answering my own question<br>The eVC compiler does not optomise for shifts on source rgisters when compiling ARM code<br>a=b+(c<<8)<br>compiles to:<br>mov r1, r2, lsl #8<br>add r3, r0, r1<br><br>As opposed to:<br>add r3,r0,r2 lsl #8<br>hmmm bad Microsoft <br>BTW<br>it would not be too difficult to go through by hand and correct this by hand for anyone doing an amount of fixed point maths thats using alot of shifting.<br>The same is true for the indexd addressing on LDR/STR<br>LDR r0,[r2,r3 lsr #2]<br>omg im sad but i just love the code.<br>

[Digby]

How would you go about correcting this by hand?  Since the ARM compiler shipped with eVC doesn't support inline assembly language, you'll have to write a function to do this in a separate .asm file.  The function overhead would negate any win you'll get.  The only way to get the speed up you're talking about is to code the entire function that uses fixed-point in assembly language.  Or perhaps you could munge the .obj (yikes)?<br>

[simonjacobs]

But couldnt you compile your c/c++ to asm, edit the asm file, then compile to machine code?<br><br>Of course, it is more effort to do that <br><br>It depends how much speed you want I suppose.<br>

[Digby]

Simon,<br><br>Certainly you could do that.  However, everytime you changed anything in the C version of that function you'd have to go back and do it again.  That's not something I'd want to do.<br><br>

[simonjacobs]

Good point. I suppose you could do assembly optimization as the last stage of the project but it's hardly ideal either way. An inline assembler would come in handy!<br>

[gruk]

<br>btw. of this discussion, I have question..<br>How looks case of branch delay slots on StrongARM? Do I have to care about that when coding in assembler, like on MIPS or Sparc?<br><br>tia.<br>

[Digby]

No.