The Wall Street Journal is running a very interesting article on how after 200 years or so a coded message in a letter from Thomas Jefferson’s correspondence has been deciphered.
The message was sent to Jefferson by his friend Robert Patterson, a mathematical professor at the University of Pennsylvania and one of Jeffersons friends he corresponded with quite frequently.
Read more here.
Recently I needed a fast an reliable hash function with good statistics on distribution and I came across what is commonly known as the FNV-hash function. FNV is short for Fowler / Noll / Vo the last names of the three most prominent people contributing to the hashing function.
Basically the FNV algorithm is a very simple one but it is effective and yields astonishingly well differentiated hashes. It has been used in many different codes and both the algoritm itself and a standard source coude has been released into the public domain.
hash = offset_basis
for each octet_of_data to be hashed
hash = hash * FNV_prime
hash = hash xor octet_of_data
The above is called the FNV-1 algorithm. If the multiplication and the XOR change place we get a variant called the FNV-1a which is very similar in all aspects of the first one. I decided to implement both and hash both as 32 bit numbers and then put them together into one 64 bit number creating a very fast and even spread of hashed numbers.
Prime and offsets
- 32 bit
- Prime: 16777619 offset: 2166136261
- 64 bit
- Prime: 1099511628211 offset: 14695981039346656037
Here is a page on FNV that is a good source of information.
There is a lot of confusion among people on the net who recently bought a Nikon digital camera. So I was trying to clear up this concept once and for all. Please link to this site if you run a mailing list or similar where this question comes up now and then.
Nikkor is the brand of lenses produced by Nikon corporations. A lot of people refer to them simply as Nikon brand lenses or Nikon lenses. Don’t get confused, the trading name these lenses are sold under are Nikkor. Fortsätt läsa Nikkor Lens Designations