linux-kernel - Re: [PATCH v3 next 00/10] Implement mul_u64_u64_div_u64

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Message-ID: <20250614102717.GK2278213@noisy.programming.kicks-ass.net>
Date: Sat, 14 Jun 2025 12:27:17 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: David Laight <david.laight.linux@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
	u.kleine-koenig@...libre.com, Nicolas Pitre <npitre@...libre.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Biju Das <biju.das.jz@...renesas.com>
Subject: Re: [PATCH v3 next 00/10] Implement mul_u64_u64_div_u64_roundup()

On Sat, Jun 14, 2025 at 10:53:36AM +0100, David Laight wrote:
> The pwm-stm32.c code wants a 'rounding up' version of mul_u64_u64_div_u64().
> This can be done simply by adding 'divisor - 1' to the 128bit product.
> Implement mul_u64_add_u64_div_u64(a, b, c, d) = (a * b + c)/d based on the
> existing code.
> Define mul_u64_u64_div_u64(a, b, d) as mul_u64_add_u64_div_u64(a, b, 0, d) and
> mul_u64_u64_div_u64_roundup(a, b, d) as mul_u64_add_u64_div_u64(a, b, d-1, d).

Another way to achieve the same would to to expose the remainder of
mul_u64_64_div_u64(), no?