This means that considering our wildcard values – the bits marked with an x above – the only possible values are 8, 9, A, or B. The most common implementation nowadays is Variant 1 where the MSB0 is fixed as 1 and MSB1 is fixed as 0. We identify the variant by considering the first 1-3 most significant bits of N. The interpretation of all other bits in the UUID depends on the value of the variant. The variant field determines the layout of the information embedded in the UUID. The following table lists the currently defined versions: Variant The version number is identified by looking at the most significant 4 bits of the value in the M position. The values in the M and N locations uniquely identify the UUID version and variant respectively. Their canonical textual representation is as a series of 32 hexadecimal characters which are separated into five groups by hyphens in the form 8-4-4-4-12.Įmbedded inside this seemingly random series of hexadecimal characters is information about the UUID implementation. UUIDs, or universally unique IDentifiers, are simply 128-bit numbers used to uniquely identify items in software development. We’ll take a look at each one and we’ll step through the implementation details of Version 1 & Version 4 in a moment. The modern-day implementation of UUIDs can be tied back to RFC 4122 which introduced 5 different approaches for generating these identifiers. Today, we’ll take a look at the main aspects of the implementation and understand why UUIDs are practically unique, though an incredibly small potential for duplication exists. You’ve likely used UUIDs in projects before and assumed them to be unique.
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