Compile time string hashing

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This is a little bit late, but I succeeded in implementing a compile-time CRC32 function with the use of constexpr. The problem with it is that at the time of writing, it only works with GCC and not MSVC nor Intel compiler.

Here is the code snippet:

// CRC32 Table (zlib polynomial)
static constexpr uint32_t crc_table[256] = {
    0x00000000L, 0x77073096L, 0xee0e612cL, 0x990951baL, 0x076dc419L,
    0x706af48fL, 0xe963a535L, 0x9e6495a3L, 0x0edb8832L, 0x79dcb8a4L,
    0xe0d5e91eL, 0x97d2d988L, 0x09b64c2bL, 0x7eb17cbdL, 0xe7b82d07L,
...
};
template<size_t idx>
constexpr uint32_t crc32(const char * str)
{
    return (crc32<idx-1>(str) >> 8) ^ crc_table[(crc32<idx-1>(str) ^ str[idx]) & 0x000000FF];
}

// This is the stop-recursion function
template<>
constexpr uint32_t crc32<size_t(-1)>(const char * str)
{
    return 0xFFFFFFFF;
}

// This doesn't take into account the nul char
#define COMPILE_TIME_CRC32_STR(x) (crc32<sizeof(x) - 2>(x) ^ 0xFFFFFFFF)

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

CrcVal01 is equal to 0x335CC04A

Hope this will help you!

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