[rrd-developers] Re: Some minor changes proposal

Tobias Oetiker oetiker at ee.ethz.ch
Sun Oct 3 23:29:32 MEST 1999

Today you sent me mail regarding Re: [rrd-developers] Re: Some minor...:

*> > *> Tobi, you wrote about the "INT" operator being more general useful. 
*> > *> I do agree about that but I do think that if you only want operators
*> > *> that fall in that category you should mention it now. I'm sure that
*> > *> not only I will come up with other operators that are not-so-general :)
*> > 
*> > I have no general opinion on these issues yet ... but we might have to do
*> > some performance evaluations of rrd_graph to see if the CDEF language
*> > verbosity has a siginificant impact ... 
*> > 
*> Am I right in assuming that parsing a line is only done once?
*> (inside rrd_graph(), during "case GF_CDEF")
*> If so: performance should not suffer a lot since the operators are 
*> looked up from an array. I could be wrong -I'm no programmer- but
*> I think that "9,2,/,INT" will cost more than "9,2,DIV" even if DIV
*> would not be programmed in that first case.
*> I'm sure there are C-experts here who can do that test.

the parsing is only done once but there is a switch/case statement for
evaluating the expressions. This sitts at the most inner loop of the CDEF
function ... I am not sure what the performance implications with large
switch statements are ... guess this can be optimized beautifully by the
compiler ...


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