NAME

Math::Random::MT::Auto - Auto-seeded Mersenne Twister PRNGs

VERSION

This documentation refers to Math::Random::MT::Auto version 4.07.00.

SYNOPSIS

use strict;
use warnings;
use Math::Random::MT::Auto qw(rand irand shuffle gaussian),
                           '/dev/urandom' => 256,
                           'random_org';

# Functional interface
my $die_roll = 1 + int(rand(6));

my $coin_flip = (irand() & 1) ? 'heads' : 'tails';

my $deck = shuffle(1 .. 52);

my $rand_IQ = gaussian(15, 100);

# OO interface
my $prng = Math::Random::MT::Auto->new('SOURCE' => '/dev/random');

my $angle = $prng->rand(360);

my $decay_interval = $prng->exponential(12.4);

DESCRIPTION

The Mersenne Twister is a fast pseudorandom number generator (PRNG) that is capable of providing large volumes (> 10^6004) of "high quality" pseudorandom data to applications that may exhaust available "truly" random data sources or system-provided PRNGs such as rand.

This module provides PRNGs that are based on the Mersenne Twister. There is a functional interface to a single, standalone PRNG, and an OO interface (based on the inside-out object model) for generating multiple PRNG objects. The PRNGs are self-seeding, automatically acquiring a (19968-bit) random seed from user-selectable sources.

Random Number Deviates

In addition to integer and floating-point uniformly-distributed random number deviates (i.e., "irand" and "rand") , this module implements the following non-uniform deviates as found in Numerical Recipes in C:

  • Gaussian (normal)

  • Exponential

  • Erlang (gamma of integer order)

  • Poisson

  • Binomial

Shuffling

This module also provides a subroutine/method for shuffling data based on the Fisher-Yates shuffling algorithm.

Support for 64-bit Integers

If Perl has been compiled to support 64-bit integers (do perl -V and look for use64bitint=define), then this module will use a 64-bit-integer version of the Mersenne Twister, thus providing 64-bit random integers and 52-bit random doubles. The size of integers returned by "irand", and used by "get_seed" and "set_seed" will be sized accordingly.

Programmatically, the size of Perl's integers can be determined using the Config module:

use Config;
print("Integers are $Config{'uvsize'} bytes in length\n");

The code for this module has been optimized for speed. Under Cygwin, it's 2.5 times faster than Math::Random::MT, and under Solaris, it's more than four times faster. (Math::Random::MT fails to build under Windows.)

QUICKSTART

To use this module as a drop-in replacement for Perl's built-in rand function, just add the following to the top of your application code:

use strict;
use warnings;
use Math::Random::MT::Auto 'rand';

and then just use "rand" as you would normally. You don't even need to bother seeding the PRNG (i.e., you don't need to call "srand"), as that gets done automatically when the module is loaded by Perl.

If you need multiple PRNGs, then use the OO interface:

use strict;
use warnings;
use Math::Random::MT::Auto;

my $prng1 = Math::Random::MT::Auto->new();
my $prng2 = Math::Random::MT::Auto->new();

my $rand_num = $prng1->rand();
my $rand_int = $prng2->irand();

CAUTION: If you want to require this module, see the "Delayed Importation" section for important information.

MODULE DECLARATION

Subroutine Declarations

By default, this module does not automatically export any of its subroutines. If you want to use the standalone PRNG, then you should specify the subroutines you want to use when you declare the module:

use Math::Random::MT::Auto qw(rand irand shuffle gaussian
                              exponential erlang poisson binomial
                              srand get_seed set_seed get_state set_state);

Without the above declarations, it is still possible to use the standalone PRNG by accessing the subroutines using their fully-qualified names. For example:

my $rand = Math::Random::MT::Auto::rand();

Module Options

Seeding Sources

Starting the PRNGs with a 19968-bit random seed (312 64-bit integers or 624 32-bit integers) takes advantage of their full range of possible internal vectors states. This module attempts to acquire such seeds using several user-selectable sources.

(I would be interested to hear about other random data sources for possible inclusion in future versions of this module.)

Random Devices

Most OSs offer some sort of device for acquiring random numbers. The most common are /dev/urandom and /dev/random. You can specify the use of these devices for acquiring the seed for the PRNG when you declare this module:

use Math::Random::MT::Auto '/dev/urandom';
  # or
my $prng = Math::Random::MT::Auto->new('SOURCE' => '/dev/random');

or they can be specified when using "srand".

srand('/dev/random');
  # or
$prng->srand('/dev/urandom');

The devices are accessed in non-blocking mode so that if there is insufficient data when they are read, the application will not hang waiting for more.

File of Binary Data

Since the above devices are just files as far as Perl is concerned, you can also use random data previously stored in files (in binary format).

srand('C:\\Temp\\RANDOM.DAT');
  # or
$prng->srand('/tmp/random.dat');
Internet Sites

This module provides support for acquiring seed data from two Internet sites: random.org and HotBits. An Internet connection and LWP::UserAgent are required to utilize these sources.

use Math::Random::MT::Auto 'random_org';
  # or
use Math::Random::MT::Auto 'hotbits';

If you connect to the Internet through an HTTP proxy, then you must set the http_proxy variable in your environment when using these sources. (See "Proxy attributes" in LWP::UserAgent.)

The HotBits site will only provide a maximum of 2048 bytes of data per request. If you want to get the full seed from HotBits, then specify the hotbits source twice in the module declaration.

my $prng = Math::Random::MT::Auto->new('SOURCE' => ['hotbits',
                                                    'hotbits']);
Windows XP Random Data

Under Windows XP, you can acquire random seed data from the system.

use Math::Random::MT::Auto 'win32';

To utilize this option, you must have the Win32::API module installed.

User-defined Seeding Source

A subroutine reference may be specified as a seeding source. When called, it will be passed three arguments: A array reference where seed data is to be added, and the number of integers (64- or 32-bit as the case may be) needed.

sub MySeeder
{
    my $seed = $_[0];
    my $need = $_[1];

    while ($need--) {
        my $data = ...;      # Get seed data from your source
        ...
        push(@{$seed}, $data);
    }
}

my $prng = Math::Random::MT::Auto->new(\&MySeeder);

The default list of seeding sources is determined when the module is loaded (actually when the import function is called). Under Windows XP, win32 is added to the list. Otherwise, /dev/urandom and then /dev/random are checked. The first one found is added to the list. Finally, random_org is added.

For the functional interface to the standalone PRNG, these defaults can be overridden by specifying the desired sources when the module is declared, or through the use of the "srand" subroutine. Similarly for the OO interface, they can be overridden in the ->new() method when the PRNG is created, or later using the "srand" method.

Optionally, the maximum number of integers (64- or 32-bits as the case may be) to be acquired from a particular source may be specified:

# Get at most 1024 bytes from random.org
# Finish the seed using data from /dev/urandom
use Math::Random::MT::Auto 'random_org' => (1024 / $Config{'uvsize'}),
                           '/dev/urandom';
Delayed Seeding

Normally, the standalone PRNG is automatically seeded when the module is loaded. This behavior can be modified by supplying the :!auto (or :noauto) flag when the module is declared. (The PRNG will still be seeded using data such as time() and PID ($$), just in case.) When the :!auto option is used, the "srand" subroutine should be imported, and then run before calling any of the random number deviates.

use Math::Random::MT::Auto qw(rand srand :!auto);
  ...
srand();
  ...
my $rn = rand(10);

Delayed Importation

If you want to delay the importation of this module using require, then you need to execute its import function to complete the module's initialization:

eval {
    require Math::Random::MT::Auto;
    # Add options to the import call, as desired.
    import Math::Random::MT::Auto qw(rand random_org);
};

OBJECT CREATION

The OO interface for this module allows you to create multiple, independent PRNGs.

If your application will only be using the OO interface, then declare this module using the :!auto flag to forestall the automatic seeding of the standalone PRNG:

use Math::Random::MT::Auto ':!auto';
Math::Random::MT::Auto->new
my $prng = Math::Random::MT::Auto->new( %options );

Creates a new PRNG. With no options, the PRNG is seeded using the default sources that were determined when the module was loaded, or that were last supplied to the "srand" subroutine.

'STATE' => $prng_state

Sets the newly created PRNG to the specified state. The PRNG will then function as a clone of the RPNG that the state was obtained from (at the point when then state was obtained).

When the STATE option is used, any other options are just stored (i.e., they are not acted upon).

'SEED' => $seed_array_ref

When the STATE option is not used, this option seeds the newly created PRNG using the supplied seed data. Otherwise, the seed data is just copied to the new object.

'SOURCE' => 'source'
'SOURCE' => ['source', ...]

Specifies the seeding source(s) for the PRNG. If the STATE and SEED options are not used, then seed data will be immediately fetched using the specified sources, and used to seed the PRNG.

The source list is retained for later use by the "srand" method. The source list may be replaced by calling the "srand" method.

'SOURCES', 'SRC' and 'SRCS' can all be used as synonyms for 'SOURCE'.

The options above are also supported using lowercase and mixed-case names (e.g., 'Seed', 'src', etc.).

$obj->new
my $prng2 = $prng1->new( %options );

Creates a new PRNG in the same manner as "Math::Random::MT::Auto->new".

$obj->clone
my $prng2 = $prng1->clone();

Creates a new PRNG that is a copy of the referenced PRNG.

$obj->_rebless
$prng1->_rebless('Math::Random::MT::Auto::Subclass');

Reblesses the object into the specified class. This is an internal method that is intended for use in subclass constructors. See Math::Random::MT::Auto::Range for an example of its use by executing the following to find the location of its source code file:

perldoc -l Math::Random::MT::Auto::Range

SUBROUTINES/METHODS

When any of the functions listed below are invoked as subroutines, they operates with respect to the standalone PRNG. For example:

my $rand = rand();

When invoked as methods, they operate on the referenced PRNG object:

my $rand = $prng->rand();

For brevity, only usage examples for the functional interface are given below.

rand
my $rn = rand();
my $rn = rand($num);

Behaves exactly like Perl's built-in rand, returning a number uniformly distributed in [0, $num). ($num defaults to 1.)

NOTE: If you still need to access Perl's built-in rand function, you can do so using CORE::rand().

irand
my $int = irand();

Returns a random integer. For 32-bit integer Perl, the range is 0 to 2^32-1 (0xFFFFFFFF) inclusive. For 64-bit integer Perl, it's 0 to 2^64-1 inclusive.

This is the fastest way to obtain random numbers using this module.

shuffle
my $shuffled = shuffle($data, ...);
my $shuffled = shuffle(@data);
my $shuffled = shuffle(\@data);

Returns an array reference containing a random ordering of the supplied arguments (i.e., shuffled) by using the Fisher-Yates shuffling algorithm. If called with a single array reference (fastest method), the contents of the array are shuffled in situ.

gaussian
my $gn = gaussian();
my $gn = gaussian($sd);
my $gn = gaussian($sd, $mean);

Returns floating-point random numbers from a Gaussian (normal) distribution (i.e., numbers that fit a bell curve). If called with no arguments, the distribution uses a standard deviation of 1, and a mean of 0. Otherwise, the supplied argument(s) will be used for the standard deviation, and the mean.

exponential
my $xn = exponential();
my $xn = exponential($mean);

Returns floating-point random numbers from an exponential distribution. If called with no arguments, the distribution uses a mean of 1. Otherwise, the supplied argument will be used for the mean.

An example of an exponential distribution is the time interval between independent Poisson-random events such as radioactive decay. In this case, the mean is the average time between events. This is called the mean life for radioactive decay, and its inverse is the decay constant (which represents the expected number of events per unit time). The well known term half-life is given by mean * ln(2).

erlang
my $en = erlang($order);
my $en = erlang($order, $mean);

Returns floating-point random numbers from an Erlang distribution of specified order. The order must be a positive integer (> 0). The mean, if not specified, defaults to 1.

The Erlang distribution is the distribution of the sum of $order independent identically distributed random variables each having an exponential distribution. (It is a special case of the gamma distribution for which $order is a positive integer.) When $order = 1, it is just the exponential distribution. It is named after A. K. Erlang who developed it to predict waiting times in queuing systems.

poisson
my $pn = poisson($mean);
my $pn = poisson($rate, $time);

Returns integer random numbers (>= 0) from a Poisson distribution of specified mean (rate * time = mean). The mean must be a positive value (> 0).

The Poisson distribution predicts the probability of the number of Poisson-random events occurring in a fixed time if these events occur with a known average rate. Examples of events that can be modeled as Poisson distributions include:

The number of decays from a radioactive sample within a given
  time period.
The number of cars that pass a certain point on a road within
  a given time period.
The number of phone calls to a call center per minute.
The number of road kill found per a given length of road.
binomial
my $bn = binomial($prob, $trials);

Returns integer random numbers (>= 0) from a binomial distribution. The probability ($prob) must be between 0.0 and 1.0 (inclusive), and the number of trials must be >= 0.

The binomial distribution is the discrete probability distribution of the number of successes in a sequence of $trials independent Bernoulli trials (i.e., yes/no experiments), each of which yields success with probability $prob.

If the number of trials is very large, the binomial distribution may be approximated by a Gaussian distribution. If the average number of successes is small ($prob * $trials < 1), then the binomial distribution can be approximated by a Poisson distribution.

srand
srand();
srand('source', ...);

This (re)seeds the PRNG. It may be called anytime reseeding of the PRNG is desired (although this should normally not be needed).

When the :!auto flag is used, the srand subroutine should be called before any other access to the standalone PRNG.

When called without arguments, the previously determined/specified seeding source(s) will be used to seed the PRNG.

Optionally, seeding sources may be supplied as arguments as when using the 'SOURCE' option. (These sources will be saved and used again if srand is subsequently called without arguments).

# Get 250 integers of seed data from Hotbits,
#  and then get the rest from /dev/random
srand('hotbits' => 250, '/dev/random');

If called with integer data (a list of one or more value, or an array of values), or a reference to an array of integers, these data will be passed to "set_seed" for use in reseeding the PRNG.

NOTE: If you still need to access Perl's built-in srand function, you can do so using CORE::srand($seed).

get_seed
my $seed = get_seed();

Returns an array reference containing the seed last sent to the PRNG.

NOTE: Changing the data in the referenced array will not cause any changes in the PRNG (i.e., it will not reseed it). You need to use "srand" or "set_seed" for that.

set_seed
set_seed($seed, ...);
set_seed(@seed);
set_seed(\@seed);

When called with integer data (a list of one or more value, or an array of values), or a reference to an array of integers, these data will be used to reseed the PRNG.

Together with "get_seed", set_seed may be useful for setting up identical sequences of random numbers based on the same seed.

It is possible to seed the PRNG with more than 19968 bits of data (312 64-bit integers or 624 32-bit integers). However, doing so does not make the PRNG "more random" as 19968 bits more than covers all the possible PRNG state vectors.

get_state
my $state = get_state();

Returns an array reference containing the current state vector of the PRNG.

Note that the state vector is not a full serialization of the PRNG, which would also require information on the sources and seed.

set_state
set_state($state);

Sets a PRNG to the state contained in an array reference previously obtained using "get_state".

# Get the current state of the PRNG
my $state = get_state();

# Run the PRNG some more
my $rand1 = irand();

# Restore the previous state of the PRNG
set_state($state);

# Get another random number
my $rand2 = irand();

# $rand1 and $rand2 will be equal.

CAUTION: It should go without saying that you should not modify the values in the state vector obtained from "get_state". Doing so and then feeding it to "set_state" would be (to say the least) naughty.

In conjunction with Data::Dumper and do(file), "get_state" and "set_state" can be used to save and then reload the state vector between application runs. (See "EXAMPLES" below.)

THREAD SUPPORT

This module is thread-safe for PRNGs created through the OO interface for Perl v5.7.2 and beyond.

For Perl prior to v5.7.2, the PRNG objects created in the parent will be broken in the thread once it is created. Therefore, new PRNG objects must be created in the thread.

The standalone PRNG is not thread-safe, and hence should not be used in threaded applications.

No object sharing between threads

Due to limitations in the Perl threading model, blessed objects (i.e., objects create through OO interfaces) cannot be shared between threads. The docs on this are not worded very clearly, but here's the gist:

    When a thread is created, any blessed objects that exist will be cloned between the parent and child threads such that the two copies of the object then function independent of one another.

    However, the threading model does not support sharing blessed objects (via use threads::shared) between threads such that an object appears to be a single copy whereby changes to the object made in the one thread are visible in another thread.

Thus, the following will generate a runtime error:

use Math::Random::MT::Auto;
use threads;
use threads::shared;

my $prng;
share($prng);

$prng = Math::Random::MT::Auto->new();

and if you try turning things around a bit:

my $prng = Math::Random::MT::Auto->new();
share($prng);

you don't get an error message, but all the internals of your object are wiped out. (In this case $prng is now just a reference to an empty hash - the data placed inside it when it was created have been removed.)

(Just to be perfectly clear: This is not a deficiency in this module, but an issue with Perl's threading model in general.)

IMPLEMENTING SUBCLASSES

This package uses the inside-out object model (see informational links under "SEE ALSO"). This object model offers a number of advantages, but does require some extra programming when you create subclasses so as to support (among other things) oject cloning for thread safety (i.e., a CLONE subroutine), and oject destruction (i.e., a DESTROY subroutine).

Further, the objects created are not the usual blessed hash reference: In the case of this package, they are blessed scalar references. Therefore, your subclass cannot store attributes inside the object returned by this package. In addition, you cannot modify the value stored in the object's referenced scalar, and you should not try to make use of it in your code as the parent class can and does change its value.

The subclass Math::Random::MT::Auto::Range included with this module's distribution is provided as an example of how to implement subclasses of this package. Execute the following to find the location of its source code file:

perldoc -l Math::Random::MT::Auto::Range

EXAMPLES

Cloning the standalone PRNG to an object
use Math::Random::MT::Auto qw(rand irand get_state);

my $prng = Math::Random::MT::Auto->new('STATE' => get_state());

The standalone PRNG and the PRNG object will now return the same sequence of pseudorandom numbers.

Save state to file
use Data::Dumper;
use Math::Random::MT::Auto qw(rand irand get_state);

my $state = get_state();
if (open(my $FH, '>', '/tmp/rand_state_data.tmp')) {
    print($FH Data::Dumper->Dump([$state], ['state']));
    print($FH "1;\n");
    close($FH);
}
Use state as stored above
use Math::Random::MT::Auto qw(rand irand set_state);

our $state;
my $rc = do('/tmp/rand_state_data.tmp');
unlink('/tmp/rand_state_data.tmp');
if ($rc) {
    set_state($state);
}

Included in this module's distribution are several sample programs (located in the samples sub-directory) that illustrate the use of the various random number deviates and other features supported by this module.

DIAGNOSTICS

WARNINGS

Warnings are generated by this module primarily when problems are encountered while trying to obtain random seed data for the PRNGs. This may occur after the module is loaded, after a PRNG object is created, or after calling "srand".

These seed warnings are not critical in nature. The PRNG will still be seeded (at a minimum using data such as time() and PID ($$)), and can be used safely.

The following illustrates how such warnings can be trapped for programmatic handling:

my @WARNINGS;
BEGIN {
    $SIG{__WARN__} = sub { push(@WARNINGS, @_); };
}

use Math::Random::MT::Auto;

# Check for standalone PRNG warnings
if (@WARNINGS) {
    # Handle warnings as desired
    ...
    # Clear warnings
    undef(@WARNINGS);
}

my $prng = Math::Random::MT::Auto->new();

# Check for PRNG object warnings
if (@WARNINGS) {
    # Handle warnings as desired
    ...
    # Clear warnings
    undef(@WARNINGS);
}
  • Failure opening random device '...': ...

    The specified device (e.g., /dev/random) could not be opened by the module. Further diagnostic information should be included with this warning message (e.g., device does not exist, permission problem, etc.).

  • Failure setting non-blocking mode on random device '...': ...

    The specified device could not be set to non-blocking mode. Further diagnostic information should be included with this warning message (e.g., permission problem, etc.).

  • Failure reading from random device '...': ...

    A problem occurred while trying to read from the specified device. Further diagnostic information should be included with this warning message.

  • Random device '...' exhausted

    The specified device did not supply the requested number of random numbers for the seed. It could possibly occur if /dev/random is used too frequently. It will occur if the specified device is a file, and it does not have enough data in it.

  • Failure loading LWP::UserAgent: ...

    To utilize the option of acquiring seed data from Internet sources, you need to install the LWP::UserAgent module.

  • Failure contacting random.org: ...

  • Failure contacting HotBits: ...

  • Failure getting data from random.org: 500 Can't connect to www.random.org:80 (connect: timeout)

  • Failure getting data from HotBits: 500 Can't connect to www.fourmilab.ch:80 (connect: timeout)

    You need to have an Internet connection to utilize random.org or HotBits as random seed sources.

    If you connect to the Internet through an HTTP proxy, then you must set the http_proxy variable in your environment when using the Internet seed sources. (See "Proxy attributes" in LWP::UserAgent.)

    This module sets a 10 second timeout for Internet connections so that if something goes awry when trying to get seed data from an Internet source, your application will not hang for an inordinate amount of time.

  • You have exceeded your 24-hour quota for HotBits.

    The HotBits site has a quota on the amount of data you can request in a 24-hour period. (I don't know how big the quota is.) Therefore, this source may fail to provide any data if used too often.

  • Can't use 'win32' source: Not Win XP

  • Can't use 'win32' source: Unable to determine Windows version

  • Can't use 'win32' source: Not Win XP ...

    The win32 random data source is only available under Windows XP (and later).

  • Failure acquiring Win XP random data: ...

    A problem occurred while trying to acquire seed data from the Window XP random source. Further diagnostic information should be included with this warning message.

  • No seed data obtained from sources - Setting minimal seed using PID and time

    This message will occur in combination with some other message(s) above.

    If the module cannot acquire any seed data from the specified sources, then data such as time() and PID ($$) will be used to seed the PRNG.

  • Partial seed - only X of Y

    This message will occur in combination with some other message(s) above. It informs you of how much seed data was needed and acquired.

ERRORS

These errors indicate that there is something fubar in you code.

  • Missing argument to 'set_seed'

    "set_seed" must be called with an array ref, or a list of integer seed data.

  • 'set_state' requires an array ref

    "set_state" must be called with an array reference previously obtained using "get_state".

  • Invalid argument to Math::Random::MT::Auto->new(): Value for 'STATE' is not an array ref

    The 'STATE' argument must be an array reference previously obtained using "get_state".

  • No seed sources specified - Setting minimal seed using PID and time

    This message occurs when you require this module, but fail to execute its import function. See "Delayed Importation" for details.

  • Invalid argument to Math::Random::MT::Auto->new(): ...

    Something is messed up with your argument list to ->new().

  • Unknown seeding source: ...

    The specified seeding source is not recognized by this module. See "Seeding Sources" for more information.

PERFORMANCE

Under Cygwin, this module is 2.5 times faster than Math::Random::MT, and under Solaris, it's more than four times faster. (Math::Random::MT fails to build under Windows.) The file samples/timings.pl, included in this module's distribution, can be used to compare timing results.

If you connect to the Internet via a phone modem, acquiring seed data may take a second or so. This delay might be apparent when your application is first started, or after creating a new PRNG object. This is especially true if you specify the hotbits source twice (so as to get the full seed from the HotBits site) as this results in two accesses to the Internet. (If /dev/urandom is available on your machine, then you should definitely consider using the Internet sources only as a secondary source.)

DEPENDENCIES

A 'C' compiler is required for building this module.

Requires Perl 5.6.0 or later.

Requires Scalar::Util 1.16 or later which can be found in the Scalar-List-Utils module.

To utilize the option of acquiring seed data from Internet sources, you need to install the LWP::UserAgent module.

Under Windows XP, to utilize the option of acquiring seed data from the system's random data source, you need to install the Win32::API module.

BUGS AND LIMITATIONS

There are no known bugs in this module.

Please submit any bugs, problems, suggestions, patches, etc. to: http://rt.cpan.org/NoAuth/Bugs.html?Dist=Math-Random-MT-Auto

SEE ALSO

The Mersenne Twister is the (current) quintessential pseudorandom number generator. It is fast, and has a period of 2^19937 - 1. The Mersenne Twister algorithm was developed by Makoto Matsumoto and Takuji Nishimura. It is available in 32- and 64-bit integer versions. http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html

Wikipedia entries on the Mersenne Twister and pseudorandom number generators, in general: http://en.wikipedia.org/wiki/Mersenne_twister, and http://en.wikipedia.org/wiki/Pseudorandom_number_generator

random.org generates random numbers from radio frequency noise. http://random.org/

HotBits generates random number from a radioactive decay source. http://www.fourmilab.ch/hotbits/

OpenBSD random devices: http://www.openbsd.org/cgi-bin/man.cgi?query=arandom&sektion=4&apropos=0&manpath=OpenBSD+Current&arch=

FreeBSD random devices: http://www.freebsd.org/cgi/man.cgi?query=random&sektion=4&apropos=0&manpath=FreeBSD+5.3-RELEASE+and+Ports

Man pages for /dev/random and /dev/urandom on Unix/Linux/Cygwin/Solaris: http://www.die.net/doc/linux/man/man4/random.4.html

Windows XP random data source: http://blogs.msdn.com/michael_howard/archive/2005/01/14/353379.aspx

Fisher-Yates Shuffling Algorithm: http://en.wikipedia.org/wiki/Shuffling_playing_cards#Shuffling_algorithms, and shuffle() in List::Util

Non-uniform random number deviates in Numerical Recipes in C, Chapters 7.2 and 7.3: http://www.library.cornell.edu/nr/bookcpdf.html

Inside-out Object Model: http://www.perlmonks.org/index.pl?node_id=219378, http://www.perlmonks.org/index.pl?node_id=483162, and Chapter 15 of Perl Best Practices by Damian Conway

LWP::UserAgent

Math::Random::MT

Net::Random

AUTHOR

Jerry D. Hedden, <jdhedden AT 1979 DOT usna DOT com>

COPYRIGHT AND LICENSE

A C-Program for MT19937 (32- and 64-bit versions), with initialization improved 2002/1/26. Coded by Takuji Nishimura and Makoto Matsumoto, and including Shawn Cokus's optimizations.

Copyright (C) 1997 - 2004, Makoto Matsumoto and Takuji Nishimura,
 All rights reserved.
Copyright (C) 2005, Mutsuo Saito, All rights reserved.
Copyright 2005 Jerry D. Hedden <jdhedden AT 1979 DOT usna DOT com>

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

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Any feedback is very welcome.
m-mat AT math DOT sci DOT hiroshima-u DOT ac DOT jp
http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html