Re: [Qemu-devel] [PATCH] bitops.h: Add field32() and field64() functions to extract bitfields

[Peter Maydell]

On 26 June 2012 19:25, Blue Swirl <address@hidden> wrote:
> On Tue, Jun 26, 2012 at 6:11 PM, Peter Maydell <address@hidden> wrote:
>> On 26 June 2012 18:58, Blue Swirl <address@hidden> wrote:
>>> On Mon, Jun 25, 2012 at 7:38 PM, Peter Maydell <address@hidden> wrote:
>>>> +static inline uint64_t field64(uint64_t value, int start, int length)
>>>
>>> start and length could be unsigned.
>>
>> They could be, but is there any reason why they should be?
>> set_bit(), clear_bit() etc use 'int' for bit numbers, so this
>> is consistent with that.
>
> Negative shifts don't work, the line with assert() would get shorter
> and simpler and I like unsigned values.

I don't like using unsigned for numbers that merely happen to always
be positive (as opposed to actually requiring unsigned arithmetic)[*],
so I think I'll stick with being consistent with the existing bitops
functions, thanks :-)

[*] the classic example of where that kind of thing can trip you up
is the way it complicates the termination condition on a "for (i = N;
i >= 0; i--)" decreasing loop.

-- PMM