On Wed, Mar 12, 2025 at 9:54 AM Frederick Virchanza Gotham wrote:
>
> a) Feed sequential numbers followed by a salt into a hash algorithm such as MD5


Here's a constexpr implementation of the MD5 algorithm written by Wodann:

    https://github.com/Wodann/constexpr-md5-cpp/blob/master/include/md5.h

I've edited it a little so that the digest is a "__uint128_t" which
means it can be used as a case label:

    switch ( argc )
    {
    case uuid("I like chocolate!"):
        break;
    }

And here's how I've written a constexpr UUID generator function:

    https://godbolt.org/z/cW9K4raKz

So this means we reproducible identical builds containing compile-time
128-Bit random numbers.

Next question though is whether something along the lines of this
should be in namespace std?

And here it is copy-pasted from GodBolt:

    // Here's a constexpr implementation of the MD5 hash function
    #include "https://raw.githubusercontent.com/healytpk/md5-constexpr/refs/heads/master/include/md5.h"

    #include <source_location> // source_location
    #include <string> // string
    #include <type_traits> // is_unsigned

    // The C++ standard library hasn't got a constexpr way
    // of converting an integer to a string, hence this:
    template<typename T> requires std::is_unsigned_v<T>
    constexpr std::string uint_to_base10_string(T num)
    {
        if ( 0u == num ) return "0";
        std::string s;
        while ( num )
        {
            s.insert( s.begin(), '0' + (num % 10u) );
            num /= 10u;
        }
        return s;
    }

    // We can create a 'named' or an 'unnamed' UUID
    constexpr __uint128_t uuid( char const *const name = nullptr )
    {
        md5::details::Context c;

        auto Append =
        [&c](char const *const data) constexpr
        {
            c.append( data, md5::details::const_strlen(data) );
        };

        if ( nullptr == name )
        {
            auto const location = std::source_location::current();
            Append( location.file_name() );
            Append( location.function_name() );
            Append( uint_to_base10_string(location.line()).c_str() );
            Append( uint_to_base10_string(location.column ()).c_str() );
        }
        else
        {
            Append(name);
        }

        Append("This is my salt!");
        return c.final();
    }

    // ======================= Here's some test code =========================

    #include <iostream> // cout, endl
    #include <ios> // hex

    int main(int argc, char **argv)
    {
        switch ( argc )
        {
        case uuid("I like chocolate!"):
            break;
        }

        constexpr auto monkey = uuid("frog");
        std::cout << std::hex << (uint64_t)(monkey >> 64u) << std::endl;
    }