linux-kernel - Re: [PATCH v6 01/38] minmax: Add in

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Date:   Fri, 4 Aug 2023 03:11:25 +0800
From:   Phi Nguyen <phind.uet@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 01/38] minmax: Add in_range() macro

On 8/3/2023 9:22 PM, Matthew Wilcox wrote:
> On Thu, Aug 03, 2023 at 09:00:35PM +0800, Phi Nguyen wrote:
>> On 8/2/2023 11:13 PM, Matthew Wilcox (Oracle) wrote:
>>> +static inline bool in_range64(u64 val, u64 start, u64 len)
>>> +{
>>> +	return (val - start) < len;
>>> +}
>>> +
>>> +static inline bool in_range32(u32 val, u32 start, u32 len)
>>> +{
>>> +	return (val - start) < len;
>>> +}
>>> +
>>
>> I think these two functions return wrong result if val is smaller than start
>> and len is big enough.
> 
> How is it that you stopped reading at exactly the point where I explained
> that this is intentional?
> 
> +/**
> + * in_range - Determine if a value lies within a range.
> + * @val: Value to test.
> + * @start: First value in range.
> + * @len: Number of values in range.
> + *
> + * This is more efficient than "if (start <= val && val < (start + len))".
> + * It also gives a different answer if @start + @len overflows the size of
> + * the type by a sufficient amount to encompass @val.  Decide for yourself
> + * which behaviour you want, or prove that start + len never overflow.
> + * Do not blindly replace one form with the other.
> + */
> 

Oh, sorry, I see, my bad.