Step 6 of 6

Challenge: compile-time computation

constexpr functions can run during compilation when their inputs are constants. The result is baked into the program as a literal, and static_assert can check it. Lookup tables, hashes of fixed strings, unit conversions and configuration validation are often done this way in performance-critical code.

Since C++20, constexpr functions may use loops, local variables, std::array and even std::vector (as long as it doesn't escape).

Your turn:

• constexpr std::array<int, N> first_primes<N>(): the first N primes
• constexpr std::uint32_t hash32(std::string_view s): 32-bit FNV-1a (start 2166136261u, for each byte h ^= byte; h *= 16777619u;)

Both must work at compile time: the tests use them inside static_assert.

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