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Subject: Re: [PATCH] bitfield: add FIELD_PREP_CONST()
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Alexander Lobakin <alexandr.lobakin@intel.com>
Cc:     linux-wireless@vger.kernel.org
Date:   Wed, 18 Jan 2023 19:03:24 +0100
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On Wed, 2023-01-18 at 17:49 +0100, Alexander Lobakin wrote:
>=20
> Aaaah right. Seems like we can't avoid introducing a separate macro for
> that. I like the idea of your patch anyways!

:)

> One note re __BF_CHECK_POW2(): can't we reuse is_power_of_2() anyhow?
> Foe example, by deriving the code of the latter into a macro and then
> using it in both?
>=20

Well, not directly - for example is_power_of_2() doesn't accept 0, while
we want to accept 0 (mask being e.g. "0xfull<<60", we already check for
mask !=3D 0).

I thought about __BUILD_BUG_ON_NOT_POWER_OF_2 but it uses BUILD_BUG_ON,
not BUILD_BUG_ON_ZERO, and BUILD_BUG_ON is nicer in most contexts ...

So you could pull out the expression "((n) & ((n) - 1)) !=3D 0" from all
four of these, but it doesn't feel worth it.

johannes