C++ High Performance

Implement and verify a compile-time hash function

In order to enable the compiler to calculate the hash-sum at compile time, we rewrite the hash_function() to take a raw null-terminated char string as parameter as an advanced class like std::string cannot be evaluated at compile time. Now, we can mark the hash_function() a constexpr:

constexpr auto hash_function(const char* str) -> size_t { 
  auto sum = size_t{0}; 
  for(auto ptr = str; *ptr != '\0'; ++ptr) 
    sum += *ptr; 
  return sum; 
} 

Now, let's invoke this with a raw literal string known at compile time:

auto hash = hash_function("abc");

Then, the compiler will generate the following piece of code, which is the sum of the ASCII values corresponding to a, b, and c (97, 98, and 99):

auto hash = ...