pcordes

4 ms·

1.
by pcordes 9y ago
Actual high-performance-computing clusters are typically used efficiently, running well-tuned code. BLAS libraries (matrix multiplication) are usually very heavily optimized. Of course, a lot of code just uses these optimized building bloc
2.
by pcordes 9y ago
You're basically asking why Intel doesn't expose their internal uops as an ISA that you can program in. See my answer on a SO question asking exactly that. https://stackoverflow.com/a/32866797/224132
3.
by pcordes 9y ago
Nice. It seems gcc/clang don't know that trick. They still divide and then check that x/3 * 3 == x. https://godbolt.org/g/V4kfuu . (So do ICC17 and MSVC CL19).
4.
by pcordes 9y ago
Presumably the usual technical meaning: https://en.wikipedia.org/wiki/Critical_section i.e. the part protected by a lock() / unlock() in multi-threaded code.
5.
by pcordes 9y ago
This is almost exactly the same as dmitryg's answer, using a state-machine the same way. It would compile to nearly the same code, but with an extra instruction to sign-extend the first char into a register before adding. You did remo
6.
by pcordes 9y ago
It's pretty ridiculous to pretend that printf is free. The crux of the matter is to concat string constants and string-representations of integers into a buffer. "buzz\n" is only 5 bytes, so you can store it in a uint64_t.
7.
by pcordes 9y ago
One common trick is to handle the %3 and %5 with down-counters that you reset to 3 or 5 when they reach zero. Or better, unroll the loop by 3 so you only need one down-counter. (Also, no, `%5` isn't "horrifically" slow when
8.
by pcordes 10y ago
I added a link to this post in an update to my answer (where I added a section about causing AVX<->SSE transition stalls, which is actually highly plausible).
9.
by pcordes 10y ago
I finally got around to re-ordering my answer to put the "cheating" ideas like gimping the compiler with atomic<uint64_t> on `-m32`, or atomic<long double>, at the end. I totally agree it was crap, but my answer just
10.
by pcordes 10y ago
That's correct; I'm sure icc has vectorized versions of those functions to inline. Each monte-carlo iteration is independent, so the code vectorizes very easily if you have a vectorized RNG and vectorized exp() and log(). (vecto
11.
by pcordes 10y ago
I'd love it if the OP would clarify what kinds of things are and aren't allowed. I voted to reopen even without that, since I thought it was an interesting question. Every rule has exceptions, and judging from the voting clearly
12.
by pcordes 10y ago
That's what I found when writing my answer on SO. The only justification I could come up with for using memory was to generate all the random numbers first, then use them later. I did include several potential microarchitectural slowd