This is a package that provides alternative pseudo-random number generators.
mt_rand() is based upon the Mersenne Twister PRNG algorithm ([L1 ], [L2 ]). This PRNG has an enormous period (in fact it is 2**19937-1 which is a Mersenne Prime, hence the name). It is also suposedly 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) - we would just need some names for these functions.
isaac_rand() uses the ISAAC algorithm [L3 ] 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.
Currently the code is available at
cvs -d:pserver:[email protected]:/cvsroot/tclsoap co Random
and the distributable files are at http://sourceforge.net/projects/tclsoap in the downloads section.
Usage
# 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
# Extended ISAAC commands
# Provide extra seed data (up to 256 values can be used)
% ::isaac::isaac seed "\x01\x02\x03\x04\x05"
# Get integers from the PRNG (must have been seeded already)
% ::isaac::isaac integer
1439929434
# Get doubles (equivalent to the expr function)
% ::isaac::isaac double
0.960589176966