I think S_alloc is little used (at least in R), but I have altered it to use memset in R-devel. As I understand it all decent compilers recognize memset calls and try to inline them with optimized code (probably even optimizing the bzero case).
On 21 Apr 2004, Douglas Bates wrote: > Prof Brian Ripley <[EMAIL PROTECTED]> writes: > ... > > Zeroing the workspace is not a requirement of the original L-BFGS-B code > > that I can see. Given that it was originally in Fortran, and Fortran > > often does zero it seems a likely symptom, but it does mean that a > > variable is being used uninitialized somewhere in the code (converted to > > C). It would be better to leave vect alone and to zero the workspace with > > a memset call in lbfgsb. (Incidentally, I don't know why S_alloc does not > > use memset -- we do require standard C and use in several other places.) > > I had planned to suggest that we use memset more widely and perhaps > add a macro Memset, defined like the current Memcpy, to R_ext/RS.h. I > felt that memset was likely to be more efficient for zeroing large > areas of memory than running a loop would be. Recently Peter Dalgaard > and Andy Liaw and I discussed this with regard to a test to see if > vectors using more than 4 GB of memory could be allocated on an > Opteron. Andy installed my suggested modification to do_makevector to > use memset for zeroing freshly allocated vectors and found that the > running time for a test on an Opteron/Linux system actually increased. > It appears that, at least on that system, memset runs a loop at the > level of characters. (You mean char* bytes? S_alloc was a byte-level loop, but looking in the headers suggest that gcc3 has optimized inlined code for memset(s, 0, n).) > I still think it would be a good idea to use memset but we would want > to do some timing comparisons to make sure we don't slow things down. That's very machine- and compiler- dependent though. -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-devel
