Tom Lane wrote: > Stephan Szabo <[EMAIL PROTECTED]> writes: > > On Mon, 2 Feb 2004, Tom Lane wrote: > >> This isn't a bug, and I see no reason to clutter the code just to shut > >> up valgrind. > > > Isn't memcpy on overlapping (even entirely overlapping) buffers undefined > > behavior unless the count is 0? > > The reason that the spec describes overlapped memcpy as undefined is > that it does not want to restrict which direction the copy occurs in > (proceeding from lower to higher memory addresses or vice versa). > memmove is constrained to do the copy in the direction that will avoid > failure when the source and destination partially overlap. But memcpy > is expected to do whichever is fastest on the particular architecture, > without concern for possible overlap. (Offhand I've never heard of a > machine where memcpy doesn't work lower-to-higher, but maybe there is > one.) > > However, when the source and destination buffers are the same, it does > not matter which direction you copy in; you are picking up and putting > down the same bytes at the same addresses no matter what order you > process the bytes in. There is no implementation in existence that will > produce an unwanted result. > > If you want to argue about dependencies on implementation details that > are theoretically undefined according to the ANSI C spec, we have tons > more beyond this one. F'r instance, depending on twos-complement > arithmetic is illegal per spec also ...
Isn't memmove() for overlaping regions? That's what my BSD manual page says. -- Bruce Momjian | http://candle.pha.pa.us [EMAIL PROTECTED] | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 ---------------------------(end of broadcast)--------------------------- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
