linux-kernel - Re: [PATCH] scsi: aic7xxx: Fix unintended sign extension issue

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Message-Id: <1540481569.3006.5.camel@linux.vnet.ibm.com>
Date:   Thu, 25 Oct 2018 16:32:49 +0100
From:   James Bottomley <jejb@...ux.vnet.ibm.com>
To:     Colin King <colin.king@...onical.com>,
        Hannes Reinecke <hare@...e.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: aic7xxx: Fix unintended sign extension issue

On Thu, 2018-10-25 at 16:13 +0100, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> In the expression "ahc_inb(ahc, port+3) << 24", the initial value is
> a u8, but is promoted to a signed int, then sign-extended to
> uint64_t.

Why is this, that's highly non intuitive?  The compiler is supposed to
promote to the biggest type, which is uint64_t and then do the
calculation

James