From -7392628885620792615 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: fc772,5cc796235bc9d4d8 X-Google-Attributes: gidfc772,public X-Google-Thread: 109fba,5cc796235bc9d4d8 X-Google-Attributes: gid109fba,public X-Google-Thread: f78e5,5cc796235bc9d4d8 X-Google-Attributes: gidf78e5,public From: "Martijn Lievaart" Subject: Re: Article on exceptions in January C++ Report Date: 1998/03/03 Message-ID: <6dhnvs$eb0@netlab.cs.rpi.edu>#1/1 X-Deja-AN: 330515528 References: <6cjhbk$ru6@netlab.cs.rpi.edu> <6cre6n$qbd@netlab.cs.rpi.edu> <6cu53k$918@netlab.cs.rpi.edu> <6d78m5$s4u@netlab.cs.rpi.edu> <6depnb$l9t@netlab.cs.rpi.edu> X-Submission-Address: c++-submit@netlab.cs.rpi.edu X-Original-Date: 3 Mar 1998 15:08:28 -0500 X-Approved-For-Group: harkness@skeptics.org comp.lang.c++.moderated Organization: XS4ALL, networking for the masses X-Auth: PGPMoose V1.1 PGP comp.std.c++ iQBFAgUANPxm7+EDnX0m9pzZAQFxtAF9Fwb2NSCkA8YAkyBSR9MsHazkvYL+RkrX xpIDs2K1j4kJH8ZEE8vdmb4nG4fPf/hv =JIrK Newsgroups: comp.lang.c++.moderated,comp.std.c++,comp.lang.c++ Roger Glover wrote in message <6depnb$l9t@netlab.cs.rpi.edu>... --8<-- >If a bitwise swap suffices, there is a way to swap without creating a >temporary or staging in registers, using only repeated application of >the >exclusive or operator: > > a ^= b; > b ^= a; // b now contains the original contents of a > a ^= b; // a now contains the original contents of b > --8<-- > >Is there a true "swapping" situation in which a bitwise swap of values >does not suffice? I cannot imagine such a situation! > Yes there is. First you have to realize that a and b *must* be references, not local values, as the original problem inhibits making copies. Now when both a and b refer to the same location, the algorith breaks. While I admit this is not likely, it is possible, so it probably will happen. This can lead to very obscure bugs. [ Send an empty e-mail to c++-help@netlab.cs.rpi.edu for info ] [ about comp.lang.c++.moderated. First time posters: do this! ] --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://reality.sgi.com/austern_mti/std-c++/faq.html ]