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.
