Can C 11 Compile-Time String Hashing Be Achieved?

Compile Time String Hashing

Question: Is it possible to compute a string's hash at compile time using C 11's new string literals?

Answer: Yes, it is possible.

The operator that would look like has not been standardized yet, but it could resemble std::hash(value) or meta_hash<"string"_meta>::value.

Implementation:

A recent implementation has been developed for GCC using constexpr to create a compile-time CRC32 function. This implementation involves creating a CRC32 table and using a recursive template function to calculate the hash.

Example:

// CRC32 Table (zlib polynomial)
static constexpr uint32_t crc_table[256] = {
    // ...
};

template<size_t idx>
constexpr uint32_t crc32(const char * str)
{
    // ...
}

// ...

#define COMPILE_TIME_CRC32_STR(x) (crc32<sizeof(x) - 2>(x) ^ 0xFFFFFFFF)

Using this macro, you can compute a compile-time CRC32 hash of a string:

enum TestEnum
{
    CrcVal01 = COMPILE_TIME_CRC32_STR("stack-overflow"),
};

Note: This implementation only works with GCC and not MSVC or Intel compilers.

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