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

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Date: Wed, 20 Dec 2023 20:02:03 +1030
From: Qu Wenruo <quwenruo.btrfs@....com>
To: David Laight <David.Laight@...LAB.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



On 2023/12/20 19:01, David Laight wrote:
> 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.

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 = 0;
> 	for (const char *sfp = "KkMmGgTtPp"; suffix != *sfp; sfp++, shift++) {
> 		if (!*sfp)
> 			return -EINVAL;
> 	}
> 	shift = shift/2 + 1 * 10;
>
> 	David
>
> -
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