Built-in functions in c++

Question

I was browsing through some codes at the end of the contest and found out that many people were using functions like __gcd(int,int) . What are these functions ? Similar functions include

__builtin_popcount(int)

__builtin_ctz(int)

__builtin_clz(int)

Where can I study about these functions ? Googling it didn't help much.

Answer 1

Those are all GCC specifics. you can read about them here: http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html#C-Extensions - but be aware, they're NOT C/C++ Standards.