compiletime_bcd.cc

// build with arm-non-eabi-g++ -std=c++20 

#include <type_traits>
#include <array>
#include <stdio.h>

constexpr int decimal_to_bcd(int x) {
    int scale = 1;
    int result = 0;
    for(size_t i = 0; i<5; i++) {
        result += scale * (x % 10);
        x /= 10;
        scale *= 16;
    }
    return result;
}

template<int N>
consteval std::array<int, N> make_bcd_table() {
      std::array<int, N> arr = {};
      for(size_t i=0; i<N; i++) {
          arr[i] = decimal_to_bcd(i);
      }
      return arr;
}

const std::array<int, 100000> bcd_table = make_bcd_table<100000>();

#if __linux__
int main() {
    printf("%05x\n", bcd_table[1337]);
}
#endif