C/C++ const(expr) tag functions

tagging.h

#ifdef __cplusplus
#include <cstddef>
#include <cstdint>
#else
#include <stddef.h>
#include <stdint.h>
#endif

/// Fastest, C, non-constexpr way to create a 64bit tag.
#define MAKE_TAG8(a, b) ((uint64_t)(a) | ((uint64_t)(b)) << 32ULL)

#ifdef __cplusplus

/// Unfortunately the C syntax `u32 x = 'abcd'` only works for 32bit literals.
/// This function is the equivalent for 64bit literals: `u64 x = makeTag8("abcd1234")`.
/// `makeTag8("01234567") <=> MAKE_TAG8('0123', '4567')`
/// @str must have a length of exactly 8 characters.
template <size_t N>
constexpr uint64_t makeTag8(const char(&str)[N])
{
    if (N != 9)
        throw;
    return ((uint64_t)str[3] << 0ULL)
        | ((uint64_t)str[2] << 8ULL)
        | ((uint64_t)str[1] << 16ULL)
        | ((uint64_t)str[0] << 24ULL)
        | ((uint64_t)str[7] << 32ULL)
        | ((uint64_t)str[6] << 40ULL)
        | ((uint64_t)str[5] << 48ULL)
        | ((uint64_t)str[4] << 56ULL);
}

/// Uses the hash function fnv1a.
template <size_t N>
constexpr uint32_t constStrHash32(const char(&str)[N])
{
    // Reference: https://gist.github.com/underscorediscovery/81308642d0325fd386237cfa3b44785c
    uint32_t hash = 0x811c9dc5;
    const uint32_t prime = 0x1000193;

    for (size_t i = 0; i < N; ++i)
    {
        const uint8_t value = str[i];
        hash = hash ^ value;
        hash *= prime;
    }

    return hash;
}

/// Uses the hash function fnv1a.
template <size_t N>
constexpr uint64_t constStrHash64(const char(&str)[N])
{
    // Reference: https://gist.github.com/underscorediscovery/81308642d0325fd386237cfa3b44785c
    uint64_t hash = 0xcbf29ce484222325ULL;
    const uint64_t prime = 0x100000001b3ULL;

    for (size_t i = 0; i < N; ++i)
    {
        const uint8_t value = str[i];
        hash = hash ^ value;
        hash *= prime;
    }

    return hash;
}

#endif