[SOLVED] ((FIRST_EXTERNAL_VECTOR + 16) & ~15) irq_vectors.h

superNewbie · 08-24-2015, 08:58 AM

Hi,

This code is in line 58:
http://lxr.free-electrons.com/source.../irq_vectors.h

I don't understand why & ~15. Could someone explain me, please?
I don't know why he didn't simply used FIRST_EXTERNAL_VECTOR + 16, which gives the same value (?)

Code:

#include <stdio.h>

#define FEV 0x20

int main(int argc, char * argv[])
{
    printf("%d\n", ~15); // 0000b
    printf("%d\n", 16 & ~15); // 16
    printf("%d\n", (FEV + 16)); // 48; 0x30; 11 0000b
    printf("%d\n", (FEV + 16) & ~15); // 48; 0x30; 11 0000b

    return 0;
}

superNewbie · 08-24-2015, 09:15 AM

That's ok.
It gives the same result in this case, but if FIRST_EXTERNAL_VECTOR changes (0x21 for example), then & ~15 is important.