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Why is 0^0 undefined?

Why UUID v1 timestamp measured from 00:00:00.00, 15 October 1582 and not the unix epoch?

  • Why was the timestamp based UUID considers time from the start of the Gregorian calendar and not the more commonly used unix epoch? RFC for UUID: http://www.ietf.org/rfc/rfc4122.txt

  • Answer:

    As per RFC-4122, a UUID should always use a 60-bit count of the number of 100-nanosecond intervals from the start of the Gregorian Calendar when operating on a system where UTC is available.  This is a standard put in place to maximize entropy in the output hash, since UUID's are intended to be unique identifiers. There are some other cases in section 4.1.4 that detail fallbacks in case there is no UTC support: http://www.ietf.org/rfc/rfc4122.txt

Mark Grey at Quora Visit the source

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One possibility: Look at the affiliation of the document author :)

Toby Thain

The UUID is largely a formalization of the GUID notation invented by Microsoft, where timestamps use the same epoch as the http://msdn.microsoft.com/en-us/library/windows/desktop/ms724284(v=vs.85).aspx.  It's safe to assume that when the RFC was authored (by Microsoft) they were strongly motivated to keep it compatible with all the GUIDs already in circulation, which meant keeping a compatible epoch. Editorial note:  One of the rather significant downsides to the choice of UUID epoch is that modern timestamps require 60-bit precision; they can't be accurately represented with http://en.wikipedia.org/wiki/Double-precision_floating-point_format.  This makes working with UUID timestamps in languages like JavaScript, where all numbers are represented in this format, problematic.

Robert Kieffer

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