undefined reference to `__lzcnt16?

Question

I have this code which I'm trying to run with GCC-TDM 1.7.4-2 using -msse4.2 (I tried msse4) with an error:

sse_lzcnt.c|7|warning: implicit declaration of function '__lzcnt16'|
sse_lzcnt.c|9|warning: too many arguments for format|
obj\Debug\sse_lzcnt.o||In function `main':|
sse_lzcnt.c|7|undefined reference to `__lzcnt16'|

An undefined reference is usually a linking error due to a missing lib file (.a ending) but the intrinsics headers don't need one?

I made sure the intrinsics headers are in the correct include directory. Heres the code,

#include <x86intrin.h>
#include <stdio.h>

int main()
{
        unsigned short __X  = 256;
        unsigned short RESULT = __lzcnt16(__X);

        printf("result: ", RESULT);

        return 0;
}

Answer 1

You need to use the gcc command line option: -mlzcnt