From: Borislav Petkov <bp@alien8.de>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Vincent Mailhol <mailhol.vincent@wanadoo.fr>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
x86@kernel.org, Peter Zijlstra <peterz@infradead.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H . Peter Anvin" <hpa@zytor.com>,
Nathan Chancellor <nathan@kernel.org>, Tom Rix <trix@redhat.com>,
linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
David Howells <dhowells@redhat.com>,
Jan Beulich <JBeulich@suse.com>,
Christophe Jaillet <christophe.jaillet@wanadoo.fr>,
Joe Perches <joe@perches.com>,
Josh Poimboeuf <jpoimboe@kernel.org>
Subject: Re: [PATCH v5 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl to evaluate constant expressions
Date: Tue, 23 Aug 2022 19:43:59 +0200 [thread overview]
Message-ID: <YwUR35I7+5JbLvMM@zn.tnic> (raw)
In-Reply-To: <CAKwvOdnc-Js8x4sv0j23crtYP73sRkNexom5ydm=r=8rYgc_5Q@mail.gmail.com>
On Tue, Aug 23, 2022 at 10:12:17AM -0700, Nick Desaulniers wrote:
> Callers of these need to guard against zero input, as the pre-existing
> comment notes:
>
> >> Undefined if no bit exists, so code should check against 0 first.
This is just silly.
And then there's
* ffs(value) returns 0 if value is 0 or the position of the first
* set bit if value is nonzero. The first (least significant) bit
* is at position 1.
*/
static __always_inline int ffs(int x)
Can we unify the two and move the guard against 0 inside the function
or, like ffs() does, have it return 0 if value is 0?
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2022-08-23 17:44 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-11 16:03 [PATCH v2 0/2] x86/asm/bitops: optimize ff{s,z} functions for constant expressions Vincent Mailhol
2022-05-11 16:03 ` [PATCH v2 1/2] x86/asm/bitops: ffs: use __builtin_ffs to evaluate " Vincent Mailhol
2022-05-11 20:56 ` Christophe JAILLET
2022-05-11 23:30 ` Vincent MAILHOL
2022-05-11 21:35 ` Nick Desaulniers
2022-05-11 23:48 ` Vincent MAILHOL
2022-05-11 16:03 ` [PATCH v2 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl " Vincent Mailhol
2022-05-11 22:20 ` Nick Desaulniers
2022-05-11 23:23 ` Vincent MAILHOL
2022-05-12 0:03 ` [PATCH v3 0/2] x86/asm/bitops: optimize ff{s,z} functions for " Vincent Mailhol
2022-05-12 0:03 ` [PATCH v3 1/2] x86/asm/bitops: ffs: use __builtin_ffs to evaluate " Vincent Mailhol
2022-05-12 0:28 ` Nick Desaulniers
2022-05-12 1:18 ` Vincent MAILHOL
2022-05-12 0:03 ` [PATCH v3 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl " Vincent Mailhol
2022-05-12 0:19 ` Nick Desaulniers
2022-05-12 1:18 ` [PATCH v4 0/2] x86/asm/bitops: optimize ff{s,z} functions for " Vincent Mailhol
2022-05-12 1:18 ` [PATCH v4 1/2] x86/asm/bitops: ffs: use __builtin_ffs to evaluate " Vincent Mailhol
2022-05-12 3:02 ` Joe Perches
2022-05-12 4:29 ` Vincent MAILHOL
2022-05-12 1:18 ` [PATCH v4 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl " Vincent Mailhol
2022-05-23 9:22 ` [PATCH v4 0/2] x86/asm/bitops: optimize ff{s,z} functions for " Vincent MAILHOL
2022-06-25 7:26 ` [RESEND PATCH " Vincent Mailhol
2022-06-25 7:26 ` [RESEND PATCH v4 1/2] x86/asm/bitops: ffs: use __builtin_ffs to evaluate " Vincent Mailhol
2022-06-25 7:26 ` [RESEND PATCH v4 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl " Vincent Mailhol
2022-07-23 15:15 ` [RESEND PATCH v4 0/2] x86/asm/bitops: optimize ff{s,z} functions for " Vincent Mailhol
2022-07-23 15:15 ` [RESEND PATCH v4 1/2] x86/asm/bitops: ffs: use __builtin_ffs to evaluate " Vincent Mailhol
2022-08-11 14:59 ` Borislav Petkov
2022-08-12 11:55 ` Vincent MAILHOL
2022-07-23 15:15 ` [RESEND PATCH v4 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl " Vincent Mailhol
2022-07-29 11:24 ` [RESEND PATCH v4 0/2] x86/asm/bitops: optimize ff{s,z} functions for " Vincent MAILHOL
2022-07-29 12:22 ` Borislav Petkov
2022-07-29 13:50 ` Vincent MAILHOL
2022-08-12 11:44 ` [PATCH v5 " Vincent Mailhol
2022-08-12 11:44 ` [PATCH v5 1/2] x86/asm/bitops: ffs: use __builtin_ffs to evaluate " Vincent Mailhol
2022-08-12 11:44 ` [PATCH v5 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl " Vincent Mailhol
2022-08-23 16:23 ` Borislav Petkov
2022-08-23 17:12 ` Nick Desaulniers
2022-08-23 17:43 ` Borislav Petkov [this message]
2022-08-23 20:31 ` Vincent MAILHOL
2022-08-24 8:43 ` Borislav Petkov
2022-08-24 12:10 ` Vincent MAILHOL
2022-08-24 13:24 ` Borislav Petkov
2022-08-26 21:32 ` Vincent MAILHOL
2022-09-07 4:06 ` Borislav Petkov
2022-09-07 5:35 ` Vincent MAILHOL
2022-09-07 8:50 ` Borislav Petkov
2022-08-31 7:57 ` [PATCH v6 0/2] x86/asm/bitops: optimize ff{s,z} functions for " Vincent Mailhol
2022-08-31 7:57 ` [PATCH v6 1/2] x86/asm/bitops: ffs: use __builtin_ffs to evaluate " Vincent Mailhol
2022-08-31 7:57 ` [PATCH v6 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl " Vincent Mailhol
2022-08-31 8:51 ` [PATCH v6 0/2] x86/asm/bitops: optimize ff{s,z} functions for " Yury Norov
2022-09-01 3:49 ` Yury Norov
2022-09-01 10:30 ` Vincent MAILHOL
2022-09-01 14:19 ` Yury Norov
2022-09-01 17:06 ` Nick Desaulniers
2022-09-02 5:34 ` Borislav Petkov
2022-09-02 0:41 ` Vincent MAILHOL
2022-09-02 1:19 ` Vincent MAILHOL
2022-09-05 0:37 ` [PATCH v7 " Vincent Mailhol
2022-09-05 0:37 ` [PATCH v7 1/2] x86/asm/bitops: ffs: use __builtin_ffs to evaluate " Vincent Mailhol
2022-09-05 0:37 ` [PATCH v7 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl " Vincent Mailhol
2022-09-06 18:26 ` [PATCH v7 0/2] x86/asm/bitops: optimize ff{s,z} functions for " Nick Desaulniers
2022-09-07 7:04 ` Nick Desaulniers
2022-09-07 7:49 ` Vincent MAILHOL
2022-09-07 9:09 ` [PATCH v8 " Vincent Mailhol
2022-09-07 9:09 ` [PATCH v8 1/2] x86/asm/bitops: ffs: use __builtin_ffs to evaluate " Vincent Mailhol
2022-09-07 9:09 ` [PATCH v8 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl " Vincent Mailhol
2022-09-20 20:00 ` [tip: x86/asm] x86/asm/bitops: Use __builtin_ctzl() " tip-bot2 for Vincent Mailhol
2022-09-20 20:00 ` [tip: x86/asm] x86/asm/bitops: Use __builtin_ffs() " tip-bot2 for Vincent Mailhol
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