Re: [libvirt] [PATCH] Replace hashing algorithm with murmurhash

On 01/25/2012 09:38 AM, Daniel P. Berrange wrote: >>> -static unsigned long virCgroupPidCode(const void *name) >>> +static int32_t virCgroupPidCode(const void *name, int32_t seed) >>> { >>> - return (unsigned long)name; >>> + unsigned long pid = (unsigned long)name; >>> + return virHashCodeGen(&pid, sizeof(pid), seed); >> >> I'm not sure if it matters, but you could shorten these two lines to >> just one: >> >> return virHashCodeGen(&name, sizeof(unsigned long), seed); > > I actually preferred the slightly more verbose style, to make > it clearer that we're actually passing in the PID as an int, > cast to a pointer, instead of an int pointer. And given the recent thread about mingw32, this is wrong anyways. There, 'unsigned long' is 32 bits, but pid_t is 64 bits, so we'd be losing information in our hash. We probably need to fix this code to be passing (void *)&pid_t and dereferencing the pointer to get to a full pid, rather than cheating with (void*)(unsigned long)pid_t and possibly losing bits (although since this is in a context of hashing, lost bits only means more chance for collision, and not a fatal algorithmic flaw).