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posted by
LaminatorX
on Sunday March 16 2014, @03:28AM
from the premature-optimization-is-the-root-of-all-evil dept.
from the premature-optimization-is-the-root-of-all-evil dept.
Subsentient writes:
"I've been writing C for quite some time, but I never followed good conventions I'm afraid, and I never payed much attention to the optimization tricks of the higher C programmers. Sure, I use const when I can, I use the pointer methods for manual string copying, I even use register for all the good that does with modern compilers, but now, I'm trying to write a C-string handling library for personal use, but I need speed, and I really don't want to use inline ASM. So, I am wondering, what would other Soylenters do to write efficient, pure, standards-compliant C?"
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(Score: 2) by frojack on Sunday March 16 2014, @10:12PM
You haven't a clue about how to quote do you?
You also assume way more than I've said.
You also assume that changes in pipe lining make all efforts at optimization useless and unnecessary. Nothing could be further from the truth. The techniques one might adopt with knowledge of current processors might be different than what you would use before, but there are many more things you can so in your code today than you could do before.
The "fast enough" mentality is exactly part of the problem.
No, you are mistaken. I've always had this sig.
(Score: 0) by Anonymous Coward on Monday March 17 2014, @12:10AM
(Score: 1, Troll) by frojack on Monday March 17 2014, @12:18AM
When the screen you post from clearly shows the supported syntax?
No, you are mistaken. I've always had this sig.
(Score: 2) by maxwell demon on Monday March 17 2014, @05:26PM
Actually <blockquote> is the old one. It worked already before Slashdot introduced <quote> with its slightly different spacing behaviour, and it never stopped working.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 1) by rev0lt on Monday March 17 2014, @05:11AM
No, not really (Tnx AC). Is that relevant to the topic?
Well, you assume I said that. I didn't. What I said was that producing a blend of optimized code for all common CPUs at a given time is complex, and one of the most obvious examples was when you had both Prescott and Pentium M in the market. Totally different CPUs in terms of optimization.
Nothing could be further from the truth. The techniques one might adopt with knowledge of current processors might be different than what you would use before
Well, I've worked extensively with handwritten and hand-optimized assembly for most (all?) Intel x86 CPUs upto Pentium4. Just because you optimize it, doesn't necessarily mean its faster (as an old fart example, think about all those integer-only Bresenham line algorithms vs having a div per pixel). And even if it is generically faster, it is usually model-specific. And it is very easy to get it to run slower (eg. by direct and indirect stalls, cache misses, branch prediction misses, etc). The Intel Optimization Manual is more than 600 pages (http://www.intel.com/content/www/us/en/architectu re-and-technology/64-ia-32-architectures-optimizat ion-manual.html), if you can generically beat a good compiler, good for you. Or you can stop wasting time and use a profiling tool like http://software.intel.com/en-us/intel-vtune-amplif ier-xe [intel.com] to have a concrete idea of what and when to optimize, instead of having to know all little details all by yourself.
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