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From: "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>
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Date: Thu, 11 Jul 2024 12:44:16 -0700
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On 7/11/2024 6:50 AM, bart wrote:
> On 11/07/2024 03:51, Lawrence D'Oliveiro wrote:
>> On Wed, 10 Jul 2024 03:16:18 -0400, James Kuyper wrote:
>>
>>> On 7/9/24 20:57, Lawrence D'Oliveiro wrote:
>>>
>>>> On Sat, 6 Jul 2024 21:34:29 -0400, James Kuyper wrote:
>>>>
>>>>> On many platforms, if _Alignof(type) is less than the word size, then
>>>>> a C pointer to that type is implemented as the combination of the
>>>>> machine address of the correct word, combined with an offset within
>>>>> that word of the first byte of that object.
>>>>
>>>> Which is a terrific idea, except it cannot be carried to its logical
>>>> conclusion (addressing of arbitrarily-aligned dynamically-defined
>>>> bitfields) because of the requirement in the C spec that the size of a
>>>> “byte” be at least 8 bits.
>>>
>>> I will grant you that I failed to mention the fact that this is a
>>> feasible way of implementing C only on platforms with a word size of 16
>>> bits or longer.
>>
>> Don’t you think C needs a better way of handling bitfields than 
>> shift-and-
>> mask?
> 
> Yes. But because it's not hard for a million programmers to each create 
> their own macros like GETBIT and SETBIT, that's not going to happen.
> 
> Although bit operations are unusual in other languages too.
[...]

Fwiw, the last time I really used them was for special lock/wait-free 
algorithms. Stealing bits from pointers and aligning and passing 
structures on special boundaries.