Re: [boost] [Reminder][Review] The review of the Boost.Guid library

From: Oliver.Kowalke_at_[hidden]
Date: 2007-05-08 00:39:21

> > How useful can seed using MAC address + time be in system with 
> > multiple cores? Shouldn't it be CoreID + time? Just image 
> you have 16 
> > cores and just one MAC address. Is  such an assumption 
> valid to make?
 
> You would need process/thread number + mac address + time

Hmm - the RFC 4122 doesn't tell anything about threads.

Version 1 UUIDs are generated according to the following algorithm:

   o  Determine the values for the UTC-based timestamp and clock
      sequence to be used in the UUID, as described in Section 4.2.1.

   o  For the purposes of this algorithm, consider the timestamp to be a
      60-bit unsigned integer and the clock sequence to be a 14-bit
      unsigned integer.  Sequentially number the bits in a field,
      starting with zero for the least significant bit.

   o  Set the time_low field equal to the least significant 32 bits
      (bits zero through 31) of the timestamp in the same order of
      significance.

   o  Set the time_mid field equal to bits 32 through 47 from the
      timestamp in the same order of significance.

   o  Set the 12 least significant bits (bits zero through 11) of the
      time_hi_and_version field equal to bits 48 through 59 from the
      timestamp in the same order of significance.

   o  Set the four most significant bits (bits 12 through 15) of the
      time_hi_and_version field to the 4-bit version number
      corresponding to the UUID version being created, as shown in the
      table above.

   o  Set the clock_seq_low field to the eight least significant bits
      (bits zero through 7) of the clock sequence in the same order of
      significance.

   o  Set the 6 least significant bits (bits zero through 5) of the
      clock_seq_hi_and_reserved field to the 6 most significant bits
      (bits 8 through 13) of the clock sequence in the same order of
      significance.

   o  Set the two most significant bits (bits 6 and 7) of the
      clock_seq_hi_and_reserved to zero and one, respectively.

   o  Set the node field to the 48-bit IEEE address in the same order of
      significance as the address.

Oliver