data::entropy(3pm) [debian man page]

Data::Entropy(3pm)					User Contributed Perl Documentation					Data::Entropy(3pm)

NAME

       Data::Entropy - entropy (randomness) management

SYNOPSIS

	       use Data::Entropy qw(entropy_source);

	       $i = entropy_source->get_int(12345);

	       use Data::Entropy qw(with_entropy_source);

	       with_entropy_source $source, sub {
		       @a = shuffle(@a);
	       };

DESCRIPTION

       This module maintains a concept of a current selection of entropy source.  Algorithms that require entropy, such as those in
       Data::Entropy::Algorithms, can use the source nominated by this module, avoiding the need for entropy source objects to be explicitly
       passed around.  This is convenient because usually one entropy source will be used for an entire program run and so an explicit entropy
       source parameter would rarely vary.  There is also a default entropy source, avoiding the need to explicitly configure a source at all.

       If nothing is done to set a source then it defaults to the use of Rijndael (AES) in counter mode (see
       Data::Entropy::RawSource::CryptCounter and Crypt::Rijndael), keyed using Perl's built-in "rand" function.  This gives a data stream that
       looks like concentrated entropy, but really only has at most the entropy of the "rand" seed.  Within a single run it is cryptographically
       difficult to detect the correlation between parts of the pseudo-entropy stream.	If more true entropy is required then it is necessary to
       configure a different entropy source.

FUNCTIONS

       entropy_source
	   Returns the current entropy source, a "Data::Entropy::Source" object.  This will be the source passed to the innermost call to
	   "with_entropy_source", if any, or otherwise the default entropy source.

       with_entropy_source SOURCE, CLOSURE
	   The SOURCE is selected, so that it will be returned by "entropy_source", and CLOSURE is called (with no arguments).	The SOURCE is
	   selected only during the dynamic scope of the call; after CLOSURE finishes, by whatever means, the previously selected entropy source
	   is restored.

	   SOURCE is normally a "Data::Entropy::Source" object.  Alternatively, it may be "undef" to cause use of the default entropy source.  It
	   may also be a reference to a function of no arguments, which will be called to generate the actual source only if required.	This
	   avoids unnecessarily initialising the source object if it is uncertain whether any entropy will be required.  The source-generating
	   closure may return a normal source or "undef", but not another function reference.

SEE ALSO

       Data::Entropy::Algorithms, Data::Entropy::Source

AUTHOR

       Andrew Main (Zefram) <zefram@fysh.org>

COPYRIGHT

       Copyright (C) 2006, 2007, 2009, 2011 Andrew Main (Zefram) <zefram@fysh.org>

LICENSE

       This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

perl v5.12.3							    2011-05-09							Data::Entropy(3pm)

Data::Entropy::Algorithms(3pm)				User Contributed Perl Documentation			    Data::Entropy::Algorithms(3pm)

NAME

       Data::Entropy::Algorithms - basic entropy-using algorithms

SYNOPSIS

	       use Data::Entropy::Algorithms
		       qw(rand_bits rand_int rand_prob);

	       $str = rand_bits(17);
	       $i = rand_int(12345);
	       $i = rand_int(Math::BigInt->new("1000000000000"));
	       $j = rand_prob(1, 2, 3);
	       $j = rand_prob([ 1, 2, 3 ]);

	       use Data::Entropy::Algorithms qw(rand_fix rand rand_flt);

	       $x = rand_fix(48);
	       $x = rand(7);
	       $x = rand_flt(0.0, 7.0);

	       use Data::Entropy::Algorithms
		       qw(pick pick_r choose choose_r shuffle shuffle_r);

	       $item = pick($item0, $item1, $item2);
	       $item = pick_r(@items);
	       @chosen = choose(3, $item0, $item1, $item2, $item3, $item4);
	       $chosen = choose_r(3, @items);
	       @shuffled = shuffle($item0, $item1, $item2, $item3, $item4);
	       $shuffled = shuffle_r(@items);

DESCRIPTION

       This module contains a collection of fundamental algorithms that use entropy.  They all use the entropy source mechanism described in
       Data::Entropy.

FUNCTIONS

       All of these functions use entropy.  The entropy source is not an explicit input in any case.  All functions use the current entropy source
       maintained by the "Data::Entropy" module.  To select an entropy source use the "with_entropy_source" function in that module, or
       alternatively do nothing to use the default source.

   Fundamental entropy extraction
       rand_bits(NBITS)
	   Returns NBITS bits of entropy, as a string of octets.  If NBITS is not a multiple of eight then the last octet in the string has its
	   most significant bits set to zero.

       rand_int(LIMIT)
	   LIMIT must be a positive integer.  Returns a uniformly-distributed random integer in the range [0, LIMIT).  LIMIT may be either a
	   native integer, a "Math::BigInt" object, or an integer-valued "Math::BigRat" object; the returned number is of the same type.

       rand_prob(PROB ...)
       rand_prob(PROBS)
	   Returns a random integer selected with non-uniform probability.  The relative probabilities are supplied as a list of non-negative
	   integers (multiple PROB arguments) or a reference to an array of integers (the PROBS argument).  The relative probabilities may be
	   native integers, "Math::BigInt" objects, or integer-valued "Math::BigRat" objects; they must all be of the same type.  At least one
	   probability value must be positive.

	   The first relative probability value (the first PROB or the first element of PROBS) is the relative probability of returning 0.  The
	   absolute probability of returning 0 is this value divided by the total of all the relative probability values.  Similarly the second
	   value controls the probability of returning 1, and so on.

   Numbers
       rand_fix(NBITS)
	   Returns a uniformly-distributed random NBITS-bit fixed-point fraction in the range [0, 1).  That is, the result is a randomly-chosen
	   multiple of 2^-NBITS, the multiplier being a random integer in the range [0, 2^NBITS).  The value is returned in the form of a native
	   floating point number, so NBITS can be at most one greater than the number of bits of significand in the floating point format.

	   With NBITS = 48 the range of output values is the same as that of the Unix "drand48" function.

       rand([LIMIT])
	   Generates a random fixed-point fraction by "rand_fix" and then multiplies it by LIMIT, returning the result.  LIMIT defaults to 1, and
	   if it is 0 then that is also treated as 1.  The length of the fixed-point fraction is 48 bits, unless that can't be represented in the
	   native floating point type, in which case the longest possible fraction will be generated instead.

	   This is a drop-in replacement for "CORE::rand": it produces exactly the same range of output values, but using the current entropy
	   source instead of a sucky PRNG with linear relationships between successive outputs.  ("CORE::rand" does the type of calculation
	   described, but using the PRNG "drand48" to generate the fixed-point fraction.)  The details of behaviour may change in the future if
	   the behaviour of "CORE::rand" changes, to maintain the match.

	   Where the source of a module can't be readily modified, it can be made to use this "rand" by an incantation such as

		   *Foreign::Module::rand = &Data::Entropy::Algorithms::rand;

	   This must be done before the module is loaded, most likely in a "BEGIN" block.  It is also possible to override "CORE::rand" for all
	   modules, by performing this similarly early:

		   *CORE::GLOBAL::rand = &Data::Entropy::Algorithms::rand;

	   This function should not be used in any new code, because the kind of output supplied by "rand" is hardly ever the right thing to use.
	   The "int(rand($n))" idiom to generate a random integer has non-uniform probabilities of generating each possible value, except when $n
	   is a power of two.  For floating point numbers, "rand" can't generate most representable numbers in its output range, and the output is
	   biased towards zero.  In new code use "rand_int" to generate integers and "rand_flt" to generate floating point numbers.

       rand_flt(MIN, MAX)
	   Selects a uniformly-distributed real number (with infinite precision) in the range [MIN, MAX] and then rounds this number to the
	   nearest representable floating point value, which it returns.  (Actually it is only as if the function worked this way: in fact it
	   never generates the number with infinite precision.	It selects between the representable floating point values with the probabilities
	   implied by this process.)

	   This can return absolutely any floating point value in the range [MIN, MAX]; both MIN and MAX themselves are possible return values.
	   All bits of the floating point type are filled randomly, so the range of values that can be returned depends on the details of the
	   floating point format.  (See Data::Float for low-level floating point utilities.)

	   The function "die"s if MIN and MAX are not both finite.  If MIN is greater than MAX then their roles are swapped: the order of the
	   limit parameters actually doesn't matter.  If the limits are identical then that value is always returned.  As a special case, if the
	   limits are positive zero and negative zero then a zero will be returned with a randomly-chosen sign.

   Combinatorics
       pick(ITEM ...)
	   Randomly selects and returns one of the ITEMs.  Each ITEM has equal probability of being selected.

       pick_r(ITEMS)
	   ITEMS must be a reference to an array.  Randomly selects and returns one of the elements of the array.  Each element has equal
	   probability of being selected.

	   This is the same operation as that performed by "pick", but using references to avoid expensive copying of arrays.

       choose(NCHOOSE, ITEM ...)
	   Randomly selects NCHOOSE of the ITEMs.  Each ITEM has equal probability of being selected.  The chosen items are returned in a list in
	   the same order in which they appeared in the argument list.

       choose_r(NCHOOSE, ITEMS)
	   ITEMS must be a reference to an array.  Randomly selects NCHOOSE of the elements in the array.  Each element has equal probability of
	   being selected.  Returns a reference to an array containing the chosen items in the same order in which they appeared in the input
	   array.

	   This is the same operation as that performed by "choose", but using references to avoid expensive copying of arrays.

       shuffle(ITEM ...)
	   Reorders the ITEMs randomly, and returns them in a list in random order.  Each possible order has equal probability.

       shuffle_r(ITEMS)
	   ITEMS must be a reference to an array.  Reorders the elements of the array randomly.  Each possible order has equal probability.
	   Returns a reference to an array containing the elements in random order.

	   This is the same operation as that performed by "shuffle", but using references to avoid expensive copying of arrays.

SEE ALSO

       Data::Entropy, Data::Entropy::Source

AUTHOR

       Andrew Main (Zefram) <zefram@fysh.org>

COPYRIGHT

       Copyright (C) 2006, 2007, 2009, 2011 Andrew Main (Zefram) <zefram@fysh.org>

LICENSE

       This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

perl v5.12.3							    2011-05-09					    Data::Entropy::Algorithms(3pm)