[webkit-dev] Git meeting notes

[Maciej Stachowiak]

On Apr 12, 2010, at 9:44 PM, Maciej Stachowiak wrote:

>
> On Apr 12, 2010, at 8:15 PM, Timothy Hatcher wrote:
>
>> Only the first 5-7 characters are needed to identify a single  
>> commit (enough of the hash prefix to be unique). So REGRESSION 
>> (96c3b0) vs REGRESSION(r12345).
>
> How long will 7 characters last before you hit the birthday paradox?

And to answer my own question (because I'm a nerd), a 7 hex digit hash  
prefix has a 50% chance of at least one pair of revisions colliding  
when there are at least 19290 revs. So we're already past the birthday  
paradox threshold to be using only 7 digits (assuming the hashes are  
uniformly distributed).

This answer brought to you by Wikipedia and Wolfram|Alpha, favorites  
of pedantic nerds everywhere:

http://en.wikipedia.org/wiki/Birthday_problem#Cast_as_a_collision_problem
http://www.wolframalpha.com/input/?i=sqrt%282*2%5E%284*7%29*ln%281%2F%281-.5%29%29%29

Regards,
Maciej