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Date: Wed, 20 Dec 2023 20:02:03 +1030
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Subject: Re: [PATCH 1/2] lib/strtox: introduce kstrtoull_suffix() helper
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To: David Laight <David.Laight@ACULAB.COM>, 'David Disseldorp'
 <ddiss@suse.de>, Qu Wenruo <wqu@suse.com>
Cc: "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>,
 Andrew Morton <akpm@linux-foundation.org>,
 Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
 Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
 "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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From: Qu Wenruo <quwenruo.btrfs@gmx.com>
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On 2023/12/20 19:01, David Laight wrote:
> From: Qu Wenruo
>> Sent: 19 December 2023 21:18
> ...
>>> How about:
>>> 	suffix =3D *endptr;
>>> 	if (!strchr(suffixes, suffix))
>>> 		return -ENIVAL;
>>> 	shift =3D 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.

Ah, got it.
Although in that case, the 1st parameter should be ("KkMmGgTtPpEe"), as
we still support "Ee", just not by default.

Thanks,
Qu
>
> 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 =3D 0;
> 	for (const char *sfp =3D "KkMmGgTtPp"; suffix !=3D *sfp; sfp++, shift++=
) {
> 		if (!*sfp)
> 			return -EINVAL;
> 	}
> 	shift =3D shift/2 + 1 * 10;
>
> 	David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK=
1 1PT, UK
> Registration No: 1397386 (Wales)