std::copy vs. std::memcpy: When is `std::copy` Faster for Copying Large Data Blocks?

Better Performance: std::copy or std::memcpy()?

In the context of programming efficiency, a common debate arises between std::memcpy() and std::copy(): which is preferable for copying large blocks of data?

Traditionally, std::memcpy() has been seen as the faster option due to its direct memory manipulation. However, recent tests have demonstrated that std::copy can not only match this performance, but even surpass it in certain scenarios.

Empirical Evidence

One study conducted extensive tests by repeatedly hashing strings using both std::copy and std::memcpy(). The results showed that std::copy consistently outperformed std::memcpy() by an average of 2.99%.

Similar tests were conducted on a MD5 hash implementation, initially yielding inconsistent results. However, after enabling link time optimization (-flto), std::copy's performance advantage over std::memcpy() became apparent, with an average gain of 0.72%.

Why std::copy Can Be Faster

The performance gains of std::copy can be attributed to several factors:

• Aggressive inlining: Optimizing compilers typically inline std::copy, while memcpy is often a separate function call.
• Type preservation: std::copy retains type information, allowing compilers to leverage optimizations based on the data type.
• Iterators: std::copy supports iterators, providing flexibility in copying data from various containers.

Conclusion

Based on the empirical evidence, it is evident that std::copy can offer superior performance over std::memcpy() in terms of speed and efficiency. Its versatility and type-safe nature make it the recommended choice for copying large blocks of data, unless there are specific requirements that necessitate the use of std::memcpy().

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