Perl Cookbook

Making Numbers Even More Random

Problem

You want to generate numbers that are more random than Perl’s random numbers. Limitations of your C library’s random number generator seeds will sometimes cause problems. The sequence of pseudo-random numbers may repeat too soon for some applications.

Solution

Use a different random number generator, such as those provided by the Math::Random and Math::TrulyRandom modules from CPAN:

use Math::TrulyRandom;
$random = truly_random_value();

use Math::Random;
$random = random_uniform();

Discussion

Perl uses the standard C library routine rand(3) to generate pseudo-random numbers. (This can be changed at build time, however.) Some implementations of the rand function return only 16-bit random numbers or have algorithmic weaknesses and may not be sufficiently random.

The Math::TrulyRandom module uses the inadequacies of your system’s timers to generate the random numbers. This takes a while, so it isn’t useful for generating a lot of random numbers.

The Math::Random module uses the randlib library to generate random numbers. It also includes a wide range of related functions.

See Also

The srand and rand functions in perlfunc(1) and Chapter 3 of Programming Perl; Section 2.7; Section 2.8; the documentation for the CPAN modules Math::Random and Math::TrulyRandom