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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCH] support >2TB SCSI disks
Date: Thu, 29 Jan 2009 15:04:25 +0000
References: <20090127224619.3ae16173@bree.surriel.com>
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To: "M. Warner Losh" <imp@bsdimp.com>
Cc: qemu-devel@nongnu.org

> : > =A0 =A0 =A0case 0:
> : > - =A0 =A0 =A0 =A0lba =3D buf[3] | (buf[2] << 8) | ((buf[1] & 0x1f) <<=
 16);
> : > + =A0 =A0 =A0 =A0lba =3D (uint64_t) buf[3] | ((uint64_t) buf[2] << 8)=
 |
> : > + =A0 =A0 =A0 =A0 =A0 =A0 =A0(((uint64_t) buf[1] & 0x1f) << 16);
> :
> : This is not required, though I guess it's harmless.
>
> Actually, I think it is required.  ANSI-C promotion rules say that a
> char or unsigned char is promoted to an int when used in an
> expression.  This causes the result to be a 32-bit number which is
> sign-extended to a 64-bit number before being assigned to lba.

Read the code again. You'll notice that the largest possible value is=20
0x001fffff, so it doesn't matter which way you extend from 32 to 64 bits.

Paul