Re: [libvirt] [PATCH] Fixed URI parsing

On 02/09/2012 10:53 AM, Laine Stump wrote: Agreed. Any libc worth their salt implements memmove by first checking for overlap, and if there is overlap, then choosing to start the move from the direction that won't be self-destructive, without using any secondary bank; and furthermore libc will optimize things into word-size chunks for faster than byte-wise motion. Furthermore, while some hardware is tuned only for forward copies, my recollection is that x86 has a rich enough instruction set to iterate the copy in either direction with equal speed. You're almost always better off calling into libc than doing a hand-rolled implementation, except in one case: POSIX currently says that memmove, memcpy, strstr, and other functions in <string.h> are not async-signal-safe. If you are paranoid, you cannot call these functions, but can instead call a hand-rolled implementation, from inside a signal handler or between fork and exec. Or, if you are like me, you will assume that this is a bug in POSIX, and that it was oversight in the standard for omitting functions that are obviously implementable in a signal-safe manner. (Actually, I think there may be a real reason why they are not listed as signal-safe - if there is hardware like x86 that has shortcut instructions like rep movs, but where the shortcut cannot be resumed if it gets interrupted midstream; but I've never seen a web site stating that such an awful hardware design exists in practice). -- Eric Blake eblake(a)redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org