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DIR:OUT; SFP:1102; SCL:1; SRVR:CY1PR07MB2460; H:CY1PR07MB2619.namprd07.prod.outlook.com; FPR:; SPF:None; LANG:en; PTR:InfoNoRecords; MX:1; A:1; received-spf: None (protection.outlook.com: janustech.com does not designate permitted sender hosts) x-microsoft-antispam-message-info: +8u0Nf0z9ZTKZieOPacE4MtnB08QGWU9/SAEBcuGqr8ohZsyvwoPakf3O2vBUt3Mv/zytSUcUn1RcJON4HuTmDaQK6eajBUFAMUoNL59c7fRw/M8/1rkXfU5TbpJ32Mbb9jPRk5Hv++z39mkFN6Fu21o+4txll6d4tCPLchaJMjSqUUjXYxOTGg5rSPPDEbrDRKR4P/tELj2XtOdaPYk8z0RaCArYdzzgGrKRQFLBbbsvwWU36360+Kf4NJN321owAhlxBN6E3wio9dlw1ZWo6Jr7cNOF/MqqUKl3mc822pD+nAFiEYEaGJ+kug7A+OM6nLex62u3ESKoSbT4m9ptvkAbBxVIezVpOCQRjYAxd4= spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM MIME-Version: 1.0 X-OriginatorOrg: janustech.com X-MS-Exchange-CrossTenant-Network-Message-Id: fe4de107-1836-437f-573c-08d6412fe425 X-MS-Exchange-CrossTenant-originalarrivaltime: 03 Nov 2018 01:58:46.9549 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 34eb020e-3cf3-43a1-afeb-f5cf1310628e X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY1PR07MB2460 X-detected-operating-system: by eggs.gnu.org: Windows 7 or 8 [fuzzy] X-Received-From: 104.47.38.123 Subject: [Qemu-devel] [PATCH] include: Add a comment to explain the origin of sizes' lookup table X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Alberto Garcia , "qemu-block@nongnu.org" , Markus Armbruster , Max Reitz , Leonid Bloch Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP 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 Reviewed-by: Eric Blake --- include/qemu/units.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/include/qemu/units.h b/include/qemu/units.h index 68a7758650..051c274ca2 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) +/* + * 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 stringified). + * It can also be used for generic shortcuts of power-of-two sizes. + * This table is generated using the AWK script below: + * + * BEGIN { + * suffix="KMGTPE"; + * for(i=10; i<64; i++) { + * val=2**i; + * s=substr(suffix, int(i/10), 1); + * n=2**(i%10); + * pad=21-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