Why Should You Ditch `std::rand()` for the New C Random Library?

Why is the new random library better than std::rand()?

Introduction

While std::rand() is a commonly used random number generator interface, the latest C version provides an extended new random library designed to address its limitations. This article examines the differences between std::rand() and the new library, highlighting advantages and performance considerations.

Drawbacks of std::rand()

Traditional rand() implementations employ Linear Congruential Generators (LCGs), which can exhibit weaknesses:

• Limited randomness in lower-order bits
• Short periods
• Low maximum value (RAND_MAX)
• Correlation between successive values

Advantages of the New Random Library

In contrast, the new random library in offers several benefits:

• High-quality Algorithms: Uses modern generators like Mersenne Twister, providing higher quality and more unpredictable randomness.
• Explicit State Management: Rand() uses a global state, which can lead to compatibility issues with multithreaded applications and reproducible simulations. The new library supports encapsulating generators in classes, allowing for multiple independent generators.
• Cross-Platform Seeding: Provides a default random_device to seed generators cross-platform, ensuring consistent output across different compilers.

Performance Comparison

The article includes a performance comparison between the older LCG-based rand() and the new Mersenne Twister-based generator. Surprisingly, the aggregate spread of random numbers generated by both methods was similar. However, the new library was significantly slower, approximately 4x slower than rand().

Recommendations

For basic applications or cases where randomness quality is not critical, std::rand() remains a viable option. However, for more demanding applications requiring high-quality and reproducible random numbers, the new random library is strongly recommended.

Performance Optimization

If performance is a concern, the article suggests using std::minstd_rand, an LCG-based generator provided by the new library, which offers a good balance between quality and performance.

Conclusion

The new random library in C addresses the limitations of std::rand() by providing higher-quality generators, explicit state management, and consistent seeding. While it may be slower in some cases, its advantages outweigh the performance drawback when randomness quality is paramount.

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