From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3A737C2BA12 for ; Fri, 3 Apr 2020 20:40:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EE2CB21D79 for ; Fri, 3 Apr 2020 20:40:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585946442; bh=A/b6WcEW+sgH9ELmZUWFVlvFcBJ6Y5ZwDFeJXrdljgM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=xV3jUGP8FenRMzS3cqEeXMP2JNzfjQhjzoVMtyVhXsmJvoVg9Orgc1YuyMR1TQrIY jEeud68qQ4fAxMLj3XV2aWHIbo13KM/NLmPvwcf/RyOqyWLL7Ozq4kO2Fry900ovKz Y0DA92c/9R/0c96MlE/klRTTOTweXvt6c/xlU8bA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728362AbgDCUkl (ORCPT ); Fri, 3 Apr 2020 16:40:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:36786 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728108AbgDCUkk (ORCPT ); Fri, 3 Apr 2020 16:40:40 -0400 Received: from pali.im (pali.im [31.31.79.79]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id A98F621D6C; Fri, 3 Apr 2020 20:40:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585946439; bh=A/b6WcEW+sgH9ELmZUWFVlvFcBJ6Y5ZwDFeJXrdljgM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=KCtSW77DmOIggT9pPUwNw/yxTO2kMUimvir19ZiIiCURT6k8tIAOAnJeo20VJE6PJ 8TneIQB00aX2wLWdofO3lisn97vK/2swAHw2d1a9lPIq3aoEoVBRnd/nR2fnU1550R fB84Qety3Ov5CLHFyr/lEOEBm1MRkZajQBFLSS4w= Received: by pali.im (Postfix) id 9DB575DE; Fri, 3 Apr 2020 22:40:37 +0200 (CEST) Date: Fri, 3 Apr 2020 22:40:37 +0200 From: Pali =?utf-8?B?Um9ow6Fy?= To: "Kohada.Tetsuhiro@dc.MitsubishiElectric.co.jp" Cc: "'linux-fsdevel@vger.kernel.org'" , "'linux-kernel@vger.kernel.org'" , "'namjae.jeon@samsung.com'" , "'sj1557.seo@samsung.com'" , "'viro@zeniv.linux.org.uk'" Subject: Re: [PATCH 1/4] exfat: Simplify exfat_utf8_d_hash() for code points above U+FFFF Message-ID: <20200403204037.hs4ae6cl3osogrso@pali> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday 03 April 2020 02:18:15 Kohada.Tetsuhiro@dc.MitsubishiElectric.co.jp wrote: > > I guess it was designed for 8bit types, not for long (64bit types) and > > I'm not sure how effective it is even for 16bit types for which it is > > already used. > > In partial_name_hash (), when 8bit value or 16bit value is specified, > upper 8-12bits tend to be 0. > > > So question is, what should we do for either 21bit number (one Unicode > > code point = equivalent of UTF-32) or for sequence of 16bit numbers > > (UTF-16)? > > If you want to get an unbiased hash value by specifying an 8 or 16-bit value, Hello! In exfat we have sequence of 21-bit values (not 8, not 16). > the hash32() function is a good choice. > ex1: Prepare by hash32 () function. > hash = partial_name_hash (hash32 (val16,32), hash); > ex2: Use the hash32() function directly. > hash + = hash32 (val16,32); Did you mean hash_32() function from linux/hash.h? > > partial_name_hash(unsigned long c, unsigned long prevhash) > > { > > return (prevhash + (c << 4) + (c >> 4)) * 11; > > } > > Another way may replace partial_name_hash(). > > return prevhash + hash32(c,32) >