On 16/06/2016 20:01, Peter Maydell wrote: >> diff --git a/include/qemu/bitops.h b/include/qemu/bitops.h >> index 755fdd1..e411688 100644 >> --- a/include/qemu/bitops.h >> +++ b/include/qemu/bitops.h >> @@ -23,6 +23,9 @@ >> #define BIT_MASK(nr) (1UL << ((nr) % BITS_PER_LONG)) >> #define BIT_WORD(nr) ((nr) / BITS_PER_LONG) >> #define BITS_TO_LONGS(nr) DIV_ROUND_UP(nr, BITS_PER_BYTE * >> sizeof(long)) >> +/* e.g. BIT_RANGE(15, 0) -> 0xff00 */ >> +#define BIT_RANGE(hb, lb) ((2ull << (hb)) - (1ull << (lb))) > > Isn't this undefined behaviour if the hb is 63?
No, these are unsigned values so there's no undefined behavior. > I prefer a "start, length" macro to "position, position", > because this matches what we already have for the deposit > and extract functions in this header. That's fine too, albeit in the case of this patch the code would be uglier. Also, if you want a "start, length" mask you could always deposit -1 into 0... Paolo
