How Can I Generate Uniformly Distributed Random Integers in C ?

Generating Uniformly Distributed Random Integers

When developing software, generating random integers within a specified range is a common task. However, finding a fast and uniformly distributed random number generator can be challenging. In this article, we address this issue by exploring various approaches to generating random integers within a given range.

A Simple Approach

A common method for generating random integers is to use the rand() function. However, as expressed in the original question, rand() can lead to a biased distribution, especially for small ranges.

To address this issue, an alternative formula was proposed:

( (max - min) * rand() + (RAND_MAX / (2 * (max - min))) ) / RAND_MAX

While this formula provides a more uniform distribution, it still falls short of addressing all the requirements, namely, speed, uniform distribution, variable ranges, and seedability.

The C Standard Library to the Rescue

Introducing the C standard library function std::uniform_int_distribution and its associated random number generator std::mt19937. This approach is straightforward, fast, and provides unbiased results.

#include <random>

std::random_device rd;
std::mt19937 rng(rd());
std::uniform_int_distribution<int> uni(min,max);

auto random_integer = uni(rng);

The std::random_device initializes the generator with a real entropy source, ensuring that the generated numbers are unpredictable and random. The std::uniform_int_distribution defines the range of integers to be generated, guaranteeing that all values within that range have an equal probability of being selected.

This approach fulfills all the requirements:

• Speed: The standard library implementation is highly efficient, even for generating large amounts of random numbers.
• Uniform distribution: The std::uniform_int_distribution function assures an unbiased and uniform distribution of generated numbers.
• Variable ranges: The distribution can be customized to any range of integers by setting the min and max parameters.
• Seedability: The rd parameter provides a means to seed the generator with a specific value, allowing for reproducibility.

A Superior Solution

In conclusion, the simplest and best approach for generating uniformly distributed random integers in C is to use the std::uniform_int_distribution and std::mt19937 functions. This approach leverages the optimized algorithms of the standard library, ensuring both speed and randomness.

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