Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756983Ab2BHSiX (ORCPT ); Wed, 8 Feb 2012 13:38:23 -0500 Received: from am1ehsobe001.messaging.microsoft.com ([213.199.154.204]:39221 "EHLO AM1EHSOBE005.bigfish.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751197Ab2BHSiV (ORCPT ); Wed, 8 Feb 2012 13:38:21 -0500 X-SpamScore: 0 X-BigFish: VPS0(zzzz1202hzz8275bhz2fh668h839h93fh) X-Forefront-Antispam-Report: CIP:160.33.98.74;KIP:(null);UIP:(null);IPV:NLI;H:mail7.fw-bc.sony.com;RD:mail7.fw-bc.sony.com;EFVD:NLI Message-ID: <4F32C105.4060700@am.sony.com> Date: Wed, 8 Feb 2012 10:37:57 -0800 From: Tim Bird User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.12) Gecko/20100907 Fedora/3.0.7-1.fc12 Thunderbird/3.0.7 MIME-Version: 1.0 To: Greg KH , linux-embedded , linux kernel , Brian Swetland , Dima Zavin , Andrew Morton Subject: [PATCH 2/5 v2] logger: simplify and optimize get_entry_len References: <4F31DC31.6040303@am.sony.com> <4F31DDC7.1050107@am.sony.com> In-Reply-To: <4F31DDC7.1050107@am.sony.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-OriginatorOrg: am.sony.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2180 Lines: 63 Make this code slightly easier to read, and eliminate calls to sub-routines. Some of these were previously optimized away by the compiler, but one memcpy was not. In my testing, this makes the code about 20% smaller, and has no sub-routine calls and no branches (on ARM). v2 of this patch is, IMHO, easier to read than v1. Compared to that patch it uses __u8 instead of unsigned char, for consistency with the __u16 val data type, simplifies the conditional expression, adds a another comment, and moves a common statement out of the if. Signed-off-by: Tim Bird --- drivers/staging/android/logger.c | 20 ++++++++++++-------- 1 files changed, 12 insertions(+), 8 deletions(-) diff --git a/drivers/staging/android/logger.c b/drivers/staging/android/logger.c index 92456d7..3475cb7 100644 --- a/drivers/staging/android/logger.c +++ b/drivers/staging/android/logger.c @@ -93,20 +93,24 @@ static inline struct logger_log *file_get_log(struct file *file) * get_entry_len - Grabs the length of the payload of the next entry starting * from 'off'. * + * An entry length is 2 bytes (16 bits) in host endian order. + * In the log, the length does not include the size of the log entry structure. + * This function returns the size including the log entry structure. + * * Caller needs to hold log->mutex. */ static __u32 get_entry_len(struct logger_log *log, size_t off) { __u16 val; - switch (log->size - off) { - case 1: - memcpy(&val, log->buffer + off, 1); - memcpy(((char *) &val) + 1, log->buffer, 1); - break; - default: - memcpy(&val, log->buffer + off, 2); - } + /* copy 2 bytes from buffer, in memcpy order, */ + /* handling possible wrap at end of buffer */ + + ((__u8 *)&val)[0] = log->buffer[off]; + if (likely(off+1 < log->size)) + ((__u8 *)&val)[1] = log->buffer[off+1]; + else + ((__u8 *)&val)[1] = log->buffer[0]; return sizeof(struct logger_entry) + val; } -- 1.7.2.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/