----- Original Message ----- From: "Terry Golubiewski" <tjgolubi@netins.net> To: <boost@lists.boost.org> Sent: Thursday, June 03, 2010 5:38 PM Subject: Re: [boost] [boost::endian] Request for comments/interest
Tomas Puverle wrote:
Swap Based: 18 seconds Type Based 14 seconds
This is unexpected...
Swap-then-copy is less efficient than just a reverse copy (in the general case). These differences are more significant than I expected. If we allow 9 seconds for the disk i/o and memcmp, then the overhead is approximately
Type-based: 36% overhead (14-9)/14 Swap-based: 50% overhead (18-9)/18.
Been a little more conservative: If we allow 6 seconds for the disk i/o and memcmp Type-based: (14-6)=8 Swap-based: (18-6)=12. Ii.e; Swap-based spends 50% more time than Type-based.
Thanks again. If there is a performance discrepancy between swap (soon to be endian_cast<>) and the object-based approach, I will make sure to fix it, of course.
If you implement endian_cast<> using a reverse-copy instead of swapping, you will see a performance improvement.
You are right. Swap should make 50% more copies as a temporary is needed. This is in line with the figures. Vicente