linux-kernel - Re: [PATCH] bitops: add 8-bit and 16-bit rotation functions

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Message-ID: <je1w6hc6yw.fsf@sykes.suse.de>
Date:	Tue, 11 Mar 2008 21:59:35 +0100
From:	Andreas Schwab <schwab@...e.de>
To:	Segher Boessenkool <segher@...nel.crashing.org>
Cc:	Harvey Harrison <harvey.harrison@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] bitops: add 8-bit and 16-bit rotation functions

Segher Boessenkool <segher@...nel.crashing.org> writes:

>> +/**
>> + * rol16 - rotate a 16-bit value left
>> + * @word: value to rotate
>> + * @shift: bits to roll
>> + */
>> +static inline __u16 rol16(__u16 word, unsigned int shift)
>> +{
>> +	return (word << shift) | (word >> (16 - shift));
>> +}
>
> This doesn't work for shift values of 0: you get word >> 16, and
> shifts greater than or equal to the word size aren't valid C.  GCC
> will warn about this, too.

On the other hand, a value narrower than int will always be promoted
first, so this is not a problem in this case.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@...e.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
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