On 11/17/16 6:10 AM, R Smith wrote:
On 2016/11/17 10:48 AM, J Decker wrote:
https://en.wikipedia.org/wiki/Birthday_problem
/.../
one duplicate. In other words, only after generating 1 billion UUIDs
every
second for the next 100 years, the probability of creating just one
duplicate would be about 50%.
All correct, but sounding misleading... Your phrase tends to sound
like "Only after 1 billion UUIDs / sec for 100 years do I have a 50%
chance of getting a single duplicate...".
I think you miss the math. After 100 Years of generating a Billion
UUIDs/sec, we have generated a rough order of 3x10^18 UUIDs, or about
2^62 UUIDs. We have 2^128 possible UUIDs, so we are no where near 50%
chance of a duplicate for each one, and the 50% chance quoted was the
chance that in that 3x10^18 UUIDs created, there is one pair of
duplicates. (I haven't done the math to verify that number, but it is
about right, we have used about 1/2 the bits, which about the point you
expect the first duplicate)
--
Richard Damon
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