PS: you may want to research and learn how Forth interpreters are implemented, they have similar problems.
On Monday, 18 July 2016 10:30:14 UTC+3, Egon wrote: > > On Monday, 18 July 2016 03:11:29 UTC+3, ondrej...@gmail.com wrote: >> >> Cheers, I tried replicating my endeavours ( >> https://play.golang.org/p/Qxoo2ASac6), sorry if it's still too verbose. >> It's essentially rewriting the inbuilt ast.Node into a simpler nested >> struct and then walking it. >> >> In testing the performance, I started adding algebraic expressions, which >> make my walking more expensive, but don't change the 'native' expression >> evaluation (I guess due to constant folding). >> >> As to your suggestion three - I do the variable lookup in the parsing >> stage, but I still need to retain the pointer, not the value itself, >> because I'm accessing an element of that given variable (time series), and >> this element (time period) changes at runtime. >> > > https://play.golang.org/p/dd4hTpMKrp > > Of course you can additionally add constant folding and similar... > Additionally instead of working on a single float at a time, make each > variable an array of 8 floats, that are computed in parallel. > > One performance gain I can think of is to implement some pruning through >> the abovementioned constant folding and other optimisations, but I'd rather >> leave that as the last resort. Another thing that comes to mind is that I >> could return nested closures in some way - meaning that '1+3*x' would be, >> in go-like pseudocode, add(func() { return one }, func mul(func() { return >> three}, func() {return model[x]} )), where the one/tree are values passed >> to the closure when parsing the equation; but that's just now off the top >> of my head. >> >> I attached a pprof result in the header. >> >> Thanks again. >> >> On Friday, 8 July 2016 15:46:32 UTC+1, Egon wrote: >>> >>> On Friday, 8 July 2016 16:25:40 UTC+3, Ondrej wrote: >>>> >>>> Hi all, >>>> I have a model with variables, let's call them a, b, c, ..., z. These >>>> are numerical values (time series loaded from a database) and I let the >>>> user specify their relationships in a JSON, say 'z = 12; x = a + 2/3 + >>>> 3*c; >>>> y = log(12*f) + exp(g)' etc. The syntax is trivial - it's basically just >>>> algebraic relationships + a few functions (log, log2, log10, exp, >>>> trigonometrics, ...; all 1:1 mappings to their math package equivalents). >>>> >>> >>> *Tip: include a working piece of code that you want to make faster, it >>> makes it easier for people to see the problems and common issues.* >>> >>> >>>> Now, I get these relationships in a JSON and I parse them using >>>> go/parser. Then I walk the tree once and process it a bit - replacing >>>> keywords by pointers to my variable stores, replacing all the log/exp/sin >>>> with function pointers, leaving literals be literals etc. Each node is >>>> then >>>> a struct with a type and the actual contents (sadly a generic interface, >>>> because the value can be almost anything). The prep stage is now over. >>>> >>>> When actually running the model, I loop through years and within each >>>> year I solve each variable - I walk the tree and evaluate it where needed. >>>> The only non-trivial action is when I get to a model variable, I need to >>>> do >>>> a bit of lookup (it's a time series, so I need to look up the correct time >>>> period and other bits). Otherwise it's just literals, operators and >>>> function calls, all of which is fairly straightforward. >>>> >>>> This is all well and good. One of the issues is that it's rather slow. >>>> I thought it would be the recursive nature (and interface assertions), but >>>> converting all this into a shunting yard system didn't improve the >>>> performance dramatically. I've profiled the thing and removed a few >>>> hotspots, my question is not about profiling. I'm after a bit more general >>>> advice on how to handle these runtime evaluations and if there are better >>>> ways of doing so. Essentially some sort of a JIT (but Go does not have >>>> runtime assembly, right?), or maybe convert each expression into a closure >>>> or maybe a whole different algorithm or...? >>>> >>> >>> Reduce the amount of code and indirection that you need to do, few basic >>> ideas: >>> 1. implement a VM https://play.golang.org/p/dlmZ2lGPY7 >>> 2. operate on vectors of variables instead of single values >>> https://play.golang.org/p/25MIjIXs0D >>> 3. try to do the lookup of all necessary variables before starting to >>> compute with them; if possible >>> >>> Obviously pprof is your friend. ( >>> https://blog.golang.org/profiling-go-programs) >>> >>> + Egon >>> >> -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
