How to generate a sse4.2 popcnt machine instruction

Question

Using the c program:

int main(int argc , char** argv)
{

  return  __builtin_popcountll(0xf0f0f0f0f0f0f0f0);

}

and the compiler line (gcc 4.4

Answer 1

You need to do it like this:

#include 
#include 

int main(void)
{
    int pop = _mm_popcnt_u64(0xf0f0f0f0f0f0f0f0ULL);
    printf("pop = %d\n", pop);
    return 0;
}

$ gcc -Wall -m64 -msse4.2 popcnt.c -o popcnt
$ ./popcnt 
pop = 32
$ 

EDIT

Oops - I just checked the disassembly output with gcc 4.2 and ICC 11.1 - while ICC 11.1 correctly generates popcntl or popcntq, for some reason gcc does not - it calls ___popcountdi2 instead. Weird. I will try a newer version of gcc when I get a chance and see if it's fixed. I guess the only workaround otherwise is to use ICC instead of gcc.