Built-in functions in C ++

Question

I looked at some codes at the end of the contest and found out that many people use functions like __gcd(int,int) . What are these features? Similar features include

__builtin_popcount(int)

__builtin_ctz(int)

__builtin_clz(int)

Where can I find out about these features? A Google search did not help.

Answer 1

These are all the features of GCC. you can read about them here: http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html#C-Extensions - but keep in mind that they are NOT C / C ++ standards.