From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40596) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gJMoF-0004P3-4I for qemu-devel@nongnu.org; Sun, 04 Nov 2018 13:07:39 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gJMoB-0002SQ-8s for qemu-devel@nongnu.org; Sun, 04 Nov 2018 13:07:38 -0500 From: Leonid Bloch Date: Sun, 4 Nov 2018 18:07:28 +0000 Message-ID: <20181104180657.7471-2-lbloch@janustech.com> References: <20181104180657.7471-1-lbloch@janustech.com> In-Reply-To: <20181104180657.7471-1-lbloch@janustech.com> Content-Language: en-US Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Subject: [Qemu-devel] [PATCH v2 1/1] include: Add a comment to explain the origin of sizes' lookup table List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "qemu-devel@nongnu.org" , =?iso-8859-1?Q?Philippe_Mathieu-Daud=E9?= Cc: "qemu-block@nongnu.org" , Kevin Wolf , Max Reitz , Alberto Garcia , Markus Armbruster , Leonid Bloch The lookup table for power-of-two sizes was added in commit 540b8492618eb for the purpose of having convenient shortcuts for these sizes in cases when the literal number has to be present at compile time, and expressions as '(1 * KiB)' can not be used. One such case is the stringification of sizes. Beyond that, it is convenient to use these shortcuts for all power-of-two sizes, even if they don't have to be literal numbers. Despite its convenience, this table introduced 55 lines of "dumb" code, the purpose and origin of which are obscure without reading the message of the commit which introduced it. This patch fixes that by adding a comment to the code itself with a brief explanation for the reasoning behind this table. This comment includes the short AWK script that generated the table, so that anyone who's interested could make sure that the values in it are correct (otherwise these values look as if they were typed manually). Signed-off-by: Leonid Bloch --- include/qemu/units.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/include/qemu/units.h b/include/qemu/units.h index 68a7758650..1c959d182e 100644 --- a/include/qemu/units.h +++ b/include/qemu/units.h @@ -17,6 +17,24 @@ #define PiB (INT64_C(1) << 50) #define EiB (INT64_C(1) << 60) =20 +/* + * The following lookup table is intended to be used when a literal string= of + * the number of bytes is required (for example if it needs to be stringif= ied). + * It can also be used for generic shortcuts of power-of-two sizes. + * This table is generated using the AWK script below: + * + * BEGIN { + * suffix=3D"KMGTPE"; + * for(i=3D10; i<64; i++) { + * val=3D2**i; + * s=3Dsubstr(suffix, int(i/10), 1); + * n=3D2**(i%10); + * pad=3D21-int(log(n)/log(10)); + * printf("#define S_%d%siB %*d\n", n, s, pad, val); + * } + * } + */ + #define S_1KiB 1024 #define S_2KiB 2048 #define S_4KiB 4096 --=20 2.17.1