/in/foo.c: In function 'main':
/in/foo.c:21:13: warning: implicit declaration of function 'CountHw' [-Wimplicit-function-declaration]
         if (CountHw(i)) {
             ^~~~~~~
/tmp/ccsRGUoU.o: In function `main':
foo.c:(.text.startup+0x35): undefined reference to `CountHw'
collect2: error: ld returned 1 exit status