linux-kernel - RE: [PATCH 1/2] lib/strtox: introduce kstrtoull

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Date: Wed, 20 Dec 2023 08:31:48 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Qu Wenruo' <quwenruo.btrfs@....com>, 'David Disseldorp' <ddiss@...e.de>,
	Qu Wenruo <wqu@...e.com>
CC: "linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>, Andrew Morton
	<akpm@...ux-foundation.org>, Christophe JAILLET
	<christophe.jaillet@...adoo.fr>, Andy Shevchenko
	<andriy.shevchenko@...ux.intel.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/2] lib/strtox: introduce kstrtoull_suffix() helper

From: Qu Wenruo
> Sent: 19 December 2023 21:18
...
> > How about:
> > 	suffix = *endptr;
> > 	if (!strchr(suffixes, suffix))
> > 		return -ENIVAL;
> > 	shift = strcspn("KkMmGgTtPp", suffix)/2 * 10 + 10;
> 
> This means the caller has to provide the suffix string in this
> particular order.

No, The strchr() checks that the suffix is one the caller wanted.
The strcspn() is against a fixed list - so the order can be
selected to make the code shorter.

Actually strcspn() isn't the function you need.
There might be a function like strchr() that returns a count
but I can't remember its name and it may not be in kernel.
You might have to write:
	shift = 0;
	for (const char *sfp = "KkMmGgTtPp"; suffix != *sfp; sfp++, shift++) {
		if (!*sfp)
			return -EINVAL;
	}
	shift = shift/2 + 1 * 10;

	David

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