[PT] - This is a package that provides alternative pseudo-random number generators.
'''mt_rand()''' is based upon the Mersenne Twister PRNG algorithm ([http://www.math.keio.ac.jp/~matumoto/emt.html], [http://www.coyotegulch.com/algorithm/libcoyote/TwistedRoad/TwistedRoad.html]).
This PRNG has an enormous period (in fact it is 2**19937-1 which is a Mersenne Prime, hence the name).
It is also supposedly faster than the standard C library rand() function.
Furthermore, while the stock Tcl rand function generates numbers in the range (0,1),
randmt produces numbers in the range [[0,1]].
If required, it can also produce values within (0,1) as well as integer values (any 32bit value)
'''isaac_rand()''' uses the ISAAC algorithm [http://www.burtleburtle.net/bob/rand/isaacafa.html] by Bob Jenkins. ISAAC (Indirection, Shift, Accumulate, Add, and Count) generates 32-bit random numbers.
The period is guaranteed to be at least 2**40 and is 2**8295 on average.
The results are uniformly distributed, unbiased, and unpredictable unless you know the seed.
This PRNG '''is''' suitable for cryptographic use provided a suitably random seed can be provided.
'''sub_rand()''' is a subtractive random number generator.
See [Knuth], D.E. 1981, "Seminumerical Algorithms" 2nd ed. vol 2 of "The Art of Computer Programming" para: 3.2-3.3.
For each of these PRNGs a command in the ''random'' namespace exists to provide extended access.
Currently the subcommands are ''integer'', ''double'', ''seed'' and ''state'' which provide
an integer or double random number (the expr function always provides a double).
The ''seed'' subcommand lets you seed the generator with a byte array,
for example an array obtained from /dev/random.
The ''state''subcommand returns a byte array that contains the current state of the generator.
This could be used to seed the next instance of a generator.
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Currently the code is available at
cvs -d:pserver:anonymous@tclsoap.cvs.sourceforge.net:/cvsroot/tclsoap co Random
and the distributable files are at http://sourceforge.net/projects/tclsoap in the downloads section.
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'''Usage'''
package require Random
# Seed and use the Mersenne Twister PRNG
% expr {mt_srand(0)}
0.548813502432
% expr {mt_rand()}
0.592844616527
# Seed and use the ISAAC PRNG
% expr {isaac_srand(0)}
0.0943298905842
% expr {isaac_rand()}
0.187672290296
# Subtractive PRNG
% expr {sub_srand(0)}
0.53392385
% expr {sub_rand()}
0.323008803
# Extended ISAAC commands
# Provide extra seed data (up to 256 values can be used)
% ::random::isaac seed "\x01\x02\x03\x04\x05"
# Get integers from the PRNG (must have been seeded already)
% ::random::isaac integer
1439929434
# Get doubles (equivalent to the expr function)
% ::random::isaac double
0.960589176966
# Extended subtractive PRNG commands
% random::subtractive seed [string repeat \x00 3000]
% random::subtractive integer
533923850
% string length [random::subtractive state]
224
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[schlenk] A little example generating random passwords with the help of the isaac generator:
proc createPassword {{minlen 15}} {
set chars [split {abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890?:!%$*} ""]
set len [llength $chars]
set pw ""
while {[string length $pw] < $minlen} {
set rand [::random::isaac integer]
while {$rand > 0 && $minlen && [string length $pw] < $minlen} {
set rest [expr {$rand % $len}]
set rand [expr {$rand / $len}]
append pw [lindex $chars $rest]
}
}
return $pw
}
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'''random''' is also one of [TclX Commands]
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[[
[Category Mathematics] | [Category Package]
]]