On 2012-02-19 11:31-0000 arjenmar...@users.sourceforge.net wrote: > Revision: 12170 > http://plplot.svn.sourceforge.net/plplot/?rev=12170&view=rev > Author: arjenmarkus > Date: 2012-02-19 11:31:08 +0000 (Sun, 19 Feb 2012) > Log Message: > ----------- > Change the local declaration of "square* s" - the original was not accepted > by MS VC/C++.
Hi Arjen: The new declaration location is still inside two for loops so doesn't that mean at run time the memory required for s is put on the stack/removed from the stack (a->ni)*(a->nj) times, i.e., the number of iterations of the inner loop times the number of iterations of the outer loop? For large a->ni and a->nj this could become a run-time efficiency concern. In other words, isn't this an example of the general case of a statement that should be be moved outside a loop (or loops) since it doesn't depend on anything happening within the loop? I suppose a good optimizing compiler would effectively move all such statements outside of loops, but I never completely trust such optimizations. (I still vividly remember the case of the IBM fortran compiler in the 70's that calmly removed statements that _did_ depend on the loop outside of the loop when you told it to "optimize". So the programmer lore then was to never ever use the optimizer for that compiler, and it took IBM years to fix that bug.) In any case, I think it is simply a matter of good programming practice to place statements in the right location outside a loop or loops whenever we notice (as now) such statements don't depend on anything in the loop. I know this code was not your original responsibility, but since your change to separate the declaration from the assignment has made a further efficiency change possible, I think we should do that (and also in any other case where we have an obvious case of a statement in a loop that depends on nothing in the loop). Alan __________________________ Alan W. Irwin Astronomical research affiliation with Department of Physics and Astronomy, University of Victoria (astrowww.phys.uvic.ca). Programming affiliations with the FreeEOS equation-of-state implementation for stellar interiors (freeeos.sf.net); the Time Ephemerides project (timeephem.sf.net); PLplot scientific plotting software package (plplot.sf.net); the libLASi project (unifont.org/lasi); the Loads of Linux Links project (loll.sf.net); and the Linux Brochure Project (lbproject.sf.net). __________________________ Linux-powered Science __________________________ ------------------------------------------------------------------------------ Virtualization & Cloud Management Using Capacity Planning Cloud computing makes use of virtualization - but cloud computing also focuses on allowing computing to be delivered as a service. http://www.accelacomm.com/jaw/sfnl/114/51521223/ _______________________________________________ Plplot-devel mailing list Plplot-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/plplot-devel
