linux-kernel - Re: [KJ] [PATCH] is_power_of

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Date:	Fri, 16 Feb 2007 17:40:15 +0100
From:	Richard Knutsson <ricknu-0@...dent.ltu.se>
To:	Andreas Schwab <schwab@...e.de>
CC:	Vignesh Babu BM <vignesh.babu@...ro.com>,
	Kernel Janitors List <kernel-janitors@...ts.osdl.org>,
	linux-mm@...ck.org, tony.luck@...el.com,
	linux-ia64@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [KJ] [PATCH] is_power_of_2 in ia64mm

Andreas Schwab wrote:
> Richard Knutsson <ricknu-0@...dent.ltu.se> writes:
>   
>> Andreas Schwab wrote:
>>     
>>> Richard Knutsson <ricknu-0@...dent.ltu.se> writes:
>>>   
>>>       
>>>> Vignesh Babu BM wrote:
>>>>         
>>>>> @@ -175,7 +176,7 @@ static int __init hugetlb_setup_sz(char *str)
>>>>>  		tr_pages = 0x15557000UL;
>>>>>   	size = memparse(str, &str);
>>>>> -	if (*str || (size & (size-1)) || !(tr_pages & size) ||
>>>>> +	if (*str || !is_power_of_2(size) || !(tr_pages & size) ||
>>>>>  		size <= PAGE_SIZE ||
>>>>>  		size >= (1UL << PAGE_SHIFT << MAX_ORDER)) {
>>>>>  		printk(KERN_WARNING "Invalid huge page size specified\n");
>>>>>           
>>>> As we talked about before; is this really correct? !is_power_of_2(0) ==
>>>> true while (0 & (0-1)) == 0.
>>>>         
>>> size == 0 is also covered by the next two conditions, so the overall value
>>> does not change.
>>>       
>> Yes, but is it meant to state that 'size' is not a power of two?
>>     
>
> What else can it mean?
>   
What about !one_or_less_bit()? It has not been implemented (yet?) but 
been discussed. It ended by concluding that is_power_of_2() should be 
fixed up first and then we can see about it.
And as I stated before; !is_power_of_2(size) != (size & (size-1))! It 
may be a bug but then we have to be sure it is suppose to be the power of 2.

Richard Knutsson

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