Created by [CecilWesterhof].
**Getting an UUID on a *NIX System**
There are some problems with getting the [UUID] (type 4) on *NIX systems. For one they are not really random.
Because of this I created the following function:
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proc getUUIDNix {{secure False}} {
set fortyeightBits [expr {2 ** 48 - 1}]
set sixteenBits [expr {2 ** 16 - 1}]
set thirtytwoBits [expr {2 ** 32 - 1}]
set twelfBits [expr {2 ** 12 - 1}]
format %.8x-%.4x-4%.3x-%x%.3x-%.12x \ [getRandomIntInRangeNix 0 ${thirtytwoBits}] \
[getRandomIntInRangeNix 0 ${sixteenBits}] \
[getRandomIntInRangeNix 0 ${twelfBits}] \
[getRandomIntInRangeNix 8 11] \ [getRandomIntInRangeNix 0 ${twelfBits}] \
[getRandomIntInRangeNix 0 ${fortyeightBits} False True]
}
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It uses getRandomIntInRangeNix from [Random Integers].
'''A Better way'''
The above version is a straight implementation. But a more efficient implementation is:
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# An UUID is built from 5 hex strings connected by a '-'.
# Their lengths are 8, 4, 4, 4 and 12.
# With version 4 the folowing is necessary:
# - The first digit from the third string is a 4
# - The first digit from the fourth string is 8, 9, A or B.
# The five random hex strings are generated.
# The first digits of the third and fourth strings are changed.
# The UUID is build from the five strings and returned.
# Because binary scan returns lowercase letters toupper is used.
proc getUUIDNix {} {
binary scan [getRandomBytesNix 16] H8H4H4H4H12 hex1 hex2 hex3 hex4 hex5 set hex3 [string replace ${hex3} 0 0 4]
set oldVal [scan [string index ${hex4} 0] %x]
set newVal [format %X [expr {(${oldVal} & 3) | 8}]]
set hex4 [string replace ${hex4} 0 0 ${newVal}]
string toupper ${hex1}-${hex2}-${hex3}-${hex4}-${hex5}
}
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This uses getRandomBytesNix from [Get Random Bytes on *NIX].
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As always: comments, tips and questions are appreciated.
** See also **
* [UUID] for other implementations
** Discussion **
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