On Fri, Nov 16, 2007 at 01:19:13AM -0800, Alex Vinokur wrote: > On Nov 15, 1:23 pm, [EMAIL PROTECTED] (Heikki Linnakangas) > wrote: > > Alex Vinokurwrote: > > > On Nov 15, 10:40 am,Alex Vinokur<[EMAIL PROTECTED]> > > > wrote: > > > [snip] > > >> I have some question concerning Bob Jenkins' functions > > >> hashword(uint32_t*, size_t), hashlittle(uint8_t*, size_t) and > > >> hashbig(uint8_t*, size_t) in lookup3.c. > > > > >> Let k1 by a key: uint8_t* k1; strlen(k1)%sizeof(uint32_t) == 0. > > > > >> 1. hashlittle(k1) produces the same value on Little-Endian and Big- > > >> Endian machines. > > >> Let hashlittle(k1) be == L1. > > > > >> 2. hashbig(k1) produces the same value on Little-Endian and Big-Endian > > >> machines. > > >> Let hashbig(k1) be == B1. > > > > >> L1 != B1 > > > > >> 3. hashword((uint32_t*)k1) produces > > >> * L1 on LittleEndian machine and > > >> * B1 on BigEndian machine. > > > > > =================================== > > >> --------------------- > > >> The question is: is it possible to change hashword() to get > > >> * L1 on Little-Endian machine and > > >> * B1 on Big-Endian machine > > >> ? > > > > > Sorry, it should be as follows: > > > > > Is it possible to create two new hash functions on basis of > > > hashword(): > > > i) hashword_little () that produces L1 on Little-Endian and Big- > > > Endian machines; > > > ii) hashword_big () that produces B1 on Little-Endian and Big- > > > Endian machines > > > ? > > > > Why? > > > [snip] > > Suppose: > uint8_t chBuf[SIZE32 * 4]; // ((size_t)&chBuf[0] & 3) == 0 > > Function > hashlittle(chBuf, SIZE32 * 4, 0) > produces the same hashValue (let this value be L1) on little-endian > and big-endian machines. So, hashlittle() is endianness-indepent. > > On other hand, function > hashword ((uint32_t)chBuf, SIZE32, 0) > produces hashValue == L1 on little-endian machine and hashValue != L1 > on big-endian machine. So, hashword() is endianness-dependent. > > I would like to use both hashlittle() and hashword() (or > hashword_little) on little-endian and big-endian machine and to get > identical hashValues. > > > Alex Vinokur > email: alex DOT vinokur AT gmail DOT com > http://mathforum.org/library/view/10978.html > http://sourceforge.net/users/alexvn > > Alex,
As I suspected, you want a hash function that is independent of the machine endian-ness. You will need to design, develop, and test such a function yourself. As you start to look at how overflow, rot's, and shifts are handled at the boundaries you may find it difficult to get a fast hash function with those properties. Good luck. Regards, Ken ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
