Janus Dam Nielsen <[EMAIL PROTECTED]> writes: > Den 11/07/2008 kl. 22.02 skrev Martin Geisler: > >> Right, good point! We should do that. Maybe a smart compiler could >> do the necessary deductions automatically? [...] > > I am not aware of any of-the-shelf technique for this, but it would > be a fun problem to solve. > Define a cost function: > Gamma(+) = 5 > Gamma(-) = 5 > Gamma(*) = 10 > > I have no clue if these costs reflect the relative cost among the > operators, please correct me.
I have never really measured the speed of additions/subtractions, but my guess is that they are a 100 or maybe a 1000 times faster than multiplications. And comparisons are about 500 times slower than multiplications. > Given the size of an expressions that naturally appear in programs I > think it is reasonable efficient to compute all permutations of the > expression under the distributive law and then pick any one of those > with the lowest cost under the Gamma cost function. > > This is worstcase exponential, but given the size of expressions > programmers are inclined to write in a program, then I don't think > it will be a problem. For single expression I guess not, but it should also work for chains of expressions (when possible): x = a * b y = a * c z = x + y If x and y are not used, then z can be computed as a * (b + c). Was that already part of what you planned? > [...] > > If you are working in a language where you can redefine the > semantics of operators like * in Python you have to take that into > account as well, but it does not need to change the analysis > performed by the interpreter. Right, but I don't think we will want to give people that power? >> Depending on how much the SMCL compiler can do, it would be stupid >> to throw it away. But on the other hand we might be able to >> reimplement things quickly in Python from which we can work >> directly with the Python AST. I guess we need more comments from >> the Janus and Michael. > > You should see my progress report to see what the SMCL language and > compiler can do for you. I've printed the report and I hope I will have read it soon! Have you ever put up the source (and repository) somewhere? The nightly build linked from http://www.daimi.au.dk/~fagidiot/simap/ seems broken (as does many of the links on the blog...). -- Martin Geisler _______________________________________________ viff-devel mailing list (http://viff.dk/) viff-devel@viff.dk http://lists.viff.dk/listinfo.cgi/viff-devel-viff.dk
