On 05/02/11 18:25, remi.chateauneu@gmx.de wrote:
Hi,
I have a program which needs to recalculate a formula of independant arguments (doubles or integers). These arguments can be updated at any time.
This math formula is expensive to evaluate, and performance-wise it is worth, depending of which input argument changes, to recalculate only a part of the evaluation tree. Here is a simplistic exemple: z = sin(x+1)*cos(y-3) When the argument x changes, it is not necessary to recompute cos(y-3).
I wrote a prototype lib to do this, where expressions are made of cells wrapping operators, input cells and intermediate values, plus the list of depending cells.
When the value of an argument, an input cell, changes, the lib just builds the topologically sorted list of dependant cells, and reevaluates them, performing what I think is the minimum recalculation (Excel style).
(An alternate strategy is to let each data update invalidate its cell and its descendants - the actual calculation being done only when needed).
Instead of reinventing the wheel, my thought was to try to use boost::proto for this. Does it make sense ? Any code change needed please ?
Proto will help you set up the operators and functions overload for this. Then I think the best way to do this is turn the proto AST into a ordered list of cells as you said, the order being given by dependencies. Make this list a function object and have its operator() forward to cells operator() which will do the invalidation check and computation. This may require a formula type that will keep this list of cells somewhere and recall it whenever needed.