From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Shawn O. Pearce" Subject: [JGIT PATCH 3/9] Document why WindowFile's hash is *31 Date: Wed, 11 Feb 2009 18:36:53 -0800 Message-ID: <1234406219-19547-4-git-send-email-spearce@spearce.org> References: <1234406219-19547-1-git-send-email-spearce@spearce.org> <1234406219-19547-2-git-send-email-spearce@spearce.org> <1234406219-19547-3-git-send-email-spearce@spearce.org> Cc: git@vger.kernel.org To: Robin Rosenberg X-From: git-owner@vger.kernel.org Thu Feb 12 03:39:00 2009 Return-path: Envelope-to: gcvg-git-2@gmane.org Received: from vger.kernel.org ([209.132.176.167]) by lo.gmane.org with esmtp (Exim 4.50) id 1LXRTc-0002tJ-1w for gcvg-git-2@gmane.org; Thu, 12 Feb 2009 03:38:56 +0100 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757669AbZBLChK (ORCPT ); Wed, 11 Feb 2009 21:37:10 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756571AbZBLChH (ORCPT ); Wed, 11 Feb 2009 21:37:07 -0500 Received: from george.spearce.org ([209.20.77.23]:39176 "EHLO george.spearce.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756481AbZBLChD (ORCPT ); Wed, 11 Feb 2009 21:37:03 -0500 Received: by george.spearce.org (Postfix, from userid 1000) id 5723738260; Thu, 12 Feb 2009 02:37:02 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.2.4 (2008-01-01) on george.spearce.org X-Spam-Level: X-Spam-Status: No, score=-4.4 required=4.0 tests=ALL_TRUSTED,BAYES_00 autolearn=ham version=3.2.4 Received: from localhost.localdomain (localhost [127.0.0.1]) by george.spearce.org (Postfix) with ESMTP id D420E38211; Thu, 12 Feb 2009 02:37:00 +0000 (UTC) X-Mailer: git-send-email 1.6.2.rc0.204.gf6b427 In-Reply-To: <1234406219-19547-3-git-send-email-spearce@spearce.org> Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Archived-At: It doesn't really make sense on its own, but if you know about the assumption in WindowCache.hash() it all becomes a bit more clear to the reader. Signed-off-by: Shawn O. Pearce --- .../src/org/spearce/jgit/lib/WindowCache.java | 3 +++ .../src/org/spearce/jgit/lib/WindowedFile.java | 4 ++++ 2 files changed, 7 insertions(+), 0 deletions(-) diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/WindowCache.java b/org.spearce.jgit/src/org/spearce/jgit/lib/WindowCache.java index 600ebdf..0b9d20c 100644 --- a/org.spearce.jgit/src/org/spearce/jgit/lib/WindowCache.java +++ b/org.spearce.jgit/src/org/spearce/jgit/lib/WindowCache.java @@ -362,6 +362,9 @@ private static void insertLRU(final ByteWindow e) { } private static int hash(final WindowedFile wp, final int id) { + // wp.hash was already "stirred up" a bit by * 31 when + // it was created. Its reasonable to just add here. + // return ((wp.hash + id) >>> 1) % cache.length; } diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/WindowedFile.java b/org.spearce.jgit/src/org/spearce/jgit/lib/WindowedFile.java index 5eb8465..db8ea88 100644 --- a/org.spearce.jgit/src/org/spearce/jgit/lib/WindowedFile.java +++ b/org.spearce.jgit/src/org/spearce/jgit/lib/WindowedFile.java @@ -88,6 +88,10 @@ */ public WindowedFile(final File file) { fPath = file; + + // Multiply by 31 here so we can more directly combine with another + // value in WindowCache.hash(), without doing the multiply there. + // hash = System.identityHashCode(this) * 31; length = Long.MAX_VALUE; } -- 1.6.2.rc0.204.gf6b427