Unlocking the Power of Compile-Time Programming
Efficient Resource Management
When it comes to optimizing our code, every little bit counts. One area where we can make significant gains is by leveraging compile-time programming. In this article, we’ll explore how to harness this powerful technique to improve performance and reduce errors.
The Case for PrehashedString
Let’s revisit our get_bitmap_resource() function, which originally used a std::string but was later replaced with a PrehashedString. This change has a profound impact on performance, as we’ll see.
cpp
auto get_bitmap_resource(const PrehashedString& path) -> const Bitmap& {
//...
}
Uncovering the Magic of Hash Sum Calculation
To verify that our PrehashedString is indeed calculating the hash sum at compile time, we need to dig deeper. By inspecting the generated assembly code, we can confirm that the hash sum is indeed precalculated.
The Proof is in the Assembly
When we examine the assembly code generated by Clang, we find a line that corresponds to our hash sum: .quad 294 # 0x126. But what happens when we change the input string from “abc” to “aaa”? The resulting assembly code reveals the answer: .quad 291 # 0x123. This confirms that the hash sum is indeed calculated at compile time.
The Benefits of Compile-Time Programming
The examples we’ve explored demonstrate the versatility of compile-time programming. By moving expensive runtime operations to compile time, we can create faster and more efficient programs. Additionally, adding safety checks that can be verified at compile time helps us catch bugs earlier, reducing the need for exhaustive testing.
A New Era of C++ Development
In this chapter, we’ve seen how metaprogramming can be used to generate functions and values at compile time. By leveraging modern C++ features like templates, constexpr, static_assert(), and concepts, we can unlock new levels of performance and reliability. With constant string hashing, we’ve witnessed the practical application of compile-time evaluation. As we move forward, the possibilities for innovation and improvement are endless.