D - OpenMP, and set
- nicO (59/59) Aug 22 2001 I hope, i didn't make a mistake with that name.
I hope, i didn't make a mistake with that name. OpenMp are C using a some #pragma to automatically made parrallel code. It's used for highly parrallel computer (more than 1000 cpu) or for computer farm. It's the langage the most appreciate today for parrallel computing (compare to HPF (too slow) or message based library lioke PVM or ...(i forget the name) (code bloat) ). It's appreciate because of the simplicity of the C (the code could be reused with normal compiler on a normal machine). And then you could add some "pragma hint" to help the compiler to better parrallelising the code. Why puting such thing in D ? Because all new cpu could execute many instructions per cycle : 5 for the Pentuim III, 6 or 9 for current IA64. Beside that, the new cpu introduice "multimedia extention" as MMX or SSE, which are SIMD instructions (for example, multiplying 2 packet of 4 32 bits floating point number to give back a packet). In one or 2 years, will come some cpu with 2 cpu core on the same die (on the same chip), it's what is plane by AMD. Intel write very powerfull C compiler to use all this feature not provide by the C at the beginning. OpenMP provide some hint to describe how the data should be dispatch, which data should stay private to each process, which one are global to the system. (OpenMp are based on the fact that "something" simulate a shared memory computer but the hint greatly improved performance). Beside that, i think that new langage should more _describe_ what the user want to do rather than how to do it. So the compiler should compile code to the best for each cpu. It will be great not to have so many flags for compiling : the code should be enough. We compile only for debugging or for release. So it should have only 2 switchs. I have learn some langage as CASL or Machine B. This 4th generation langage are used to make prove on it. (you give a fact, and a prover say it's true or not). Make prove on C is very difficult because of the pointer and the "infinite" memory model. This kind of langage are based on mathematical finite set (ensemble in french). So prove became possible. At least, for debugging it could be useful to say : that variable are include in that set. It's very different from usual type but much more powerfull. int8 i; could be i N[0..15] (N are natural) float : fp R[0.0..15.0] (+ precision hint : a letter ? ) (R for real, but why not F but float are 32 bits for most of the user) So if the used processor have very few memory, only 4 bits need to be used. Beside that, a statical analyse of the code (i'm not saying it's easy ! ), could say : "Error, in that case, variable foobar will get out of his set". That is possible only because we manipulate finite set and not inifinite like is supposed to be in C. At least, a debug mode could just take care that some value are never reached. In case of rewriting loops, it could interresting to know how much a loop will be performed. If a loop run 5 to 8 times, it could not interresting to vectorise it (too much overhead to finish cleanly). But if the loop is always run around 10000, it's very interresting to vectorise it because the overhead are negligeable. The same thing could be used to perform strip mining properly (cut a loop into piece to increase the locality of the data, so to work as much as possible with the memory cache). I don't know how to keep C compatibility but new type will be simply to defined a new set. Some thing funny with set is that is possible to defined set of set... nicO
Aug 22 2001