On 4/21/10 10:45 AM, Simon Urbanek wrote:
Won't that miss the last incomplete chunk? (and please don't use
DATAPTR on INTSXP even though the effect is currently the same)
In general it seems that the it depends on nt whether this is
efficient or not since calls to short memcpy are expensive (very
small nt that is).
I ran some empirical tests to compare memcpy vs for() (x86_64, OS X)
and the results were encouraging - depending on the size of the
copied block the difference could be quite big: tiny block (ca. n =
32 or less) - for() is faster small block (n ~ 1k) - memcpy is ca. 8x
faster as the size increases the gap closes (presumably due to RAM
bandwidth limitations) so for n = 512M it is ~30%.
Of course this is contingent on the implementation of memcpy,
compiler, architecture etc. And will only matter if copying is what
you do most of the time ...
Copying of vectors is something that I would expect to happen fairly
often in many applications of R.
Is for() faster on small blocks by enough that one would want to branch
based on size?
+ seth
--
Seth Falcon | @sfalcon | http://userprimary.net/
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