linux-kernel - Re: [PATCH] zsmalloc: use U suffix for negative literals being shifted

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Message-ID: <20171224032437.GB5273@bombadil.infradead.org>
Date:   Sat, 23 Dec 2017 19:24:37 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Nick Desaulniers <nick.desaulniers@...il.com>
Cc:     Minchan Kim <minchan@...nel.org>, Nitin Gupta <ngupta@...are.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] zsmalloc: use U suffix for negative literals being
 shifted

On Sat, Dec 23, 2017 at 09:33:40PM -0500, Nick Desaulniers wrote:
> Fixes warnings about shifting unsigned literals being undefined
> behavior.

Do you mean signed literals?

>  			 */
> -			link->next = -1 << OBJ_TAG_BITS;
> +			link->next = -1U << OBJ_TAG_BITS;
>  		}

I don't understand what -1U means.  Seems like a contradiction in terms,
a negative unsigned number.  Is this supposed to be ~0U?