From: Jeff King <peff@peff.net>
To: git@vger.kernel.org
Cc: Shawn Pearce <spearce@spearce.org>, Jonathan Nieder <jrnieder@gmail.com>
Subject: Re: [PATCH v4 08/23] ewah: compressed bitmap implementation
Date: Thu, 23 Jan 2014 17:07:43 -0500 [thread overview]
Message-ID: <20140123220742.GA29357@sigill.intra.peff.net> (raw)
In-Reply-To: <20140123215325.GA28829@vauxhall.crustytoothpaste.net>
On Thu, Jan 23, 2014 at 09:53:26PM +0000, brian m. carlson wrote:
> On Thu, Jan 23, 2014 at 03:26:45PM -0500, Jeff King wrote:
> > Looking over the format, I think the only thing preventing 4-byte
> > alignment is the 1-byte XOR-offset and 1-byte flags field for each
> > bitmap. If we ever have a v2, we could pad the sum of those out to 4
> > bytes. Is 4-byte alignment enough? We do treat the actual data as 64-bit
> > integers. I wonder if that would have problems on Sparc64, for example.
>
> Yes, it will. SPARC requires all loads be naturally aligned (4-byte to
> an address that's a multiple of 4, 8-byte to a multiple of 8, and so
> on). In general, architectures that do not support unaligned access
> require natural alignment for all quantities.
In that case, I think we cannot even blame Shawn. The ewah serialization
format itself (which JGit inherited from the javaewah library) has 8
bytes of header and 4 bytes of trailer. So packed serialized ewahs
wouldn't be 8-byte aligned (though of course he could have added his own
padding to each when we have a sequence of them).
-Peff
next prev parent reply other threads:[~2014-01-23 22:07 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-21 13:56 [PATCH v4 0/22] pack bitmaps Jeff King
2013-12-21 13:59 ` [PATCH v4 01/23] sha1write: make buffer const-correct Jeff King
2013-12-22 9:06 ` Christian Couder
2013-12-21 13:59 ` [PATCH v4 02/23] revindex: Export new APIs Jeff King
2013-12-21 13:59 ` [PATCH v4 03/23] pack-objects: Refactor the packing list Jeff King
2013-12-21 13:59 ` [PATCH v4 04/23] pack-objects: factor out name_hash Jeff King
2013-12-21 13:59 ` [PATCH v4 05/23] revision: allow setting custom limiter function Jeff King
2013-12-21 13:59 ` [PATCH v4 06/23] sha1_file: export `git_open_noatime` Jeff King
2013-12-21 13:59 ` [PATCH v4 07/23] compat: add endianness helpers Jeff King
2013-12-21 13:59 ` [PATCH v4 08/23] ewah: compressed bitmap implementation Jeff King
2014-01-23 2:05 ` Jonathan Nieder
2014-01-23 18:33 ` Jeff King
2014-01-23 18:35 ` [PATCH 1/2] compat: move unaligned helpers to bswap.h Jeff King
2014-01-23 19:41 ` Jonathan Nieder
2014-01-23 19:44 ` Jeff King
2014-01-23 19:56 ` Jonathan Nieder
2014-01-23 20:04 ` Jeff King
2014-01-23 20:08 ` Jonathan Nieder
2014-01-23 20:09 ` Jeff King
2014-01-23 18:35 ` [PATCH 2/2] ewah: support platforms that require aligned reads Jeff King
2014-01-23 19:52 ` [PATCH v4 08/23] ewah: compressed bitmap implementation Jonathan Nieder
2014-01-23 20:03 ` Jeff King
2014-01-23 20:12 ` Jonathan Nieder
2014-01-23 20:13 ` Jeff King
2014-01-23 20:23 ` Jonathan Nieder
2014-01-23 20:29 ` Jeff King
2014-01-23 20:38 ` Jeff King
2014-01-23 20:14 ` Shawn Pearce
2014-01-23 20:26 ` Jeff King
2014-01-23 21:53 ` brian m. carlson
2014-01-23 22:07 ` Jeff King [this message]
2014-01-23 22:17 ` Jonathan Nieder
2014-01-23 22:26 ` Jeff King
2014-01-23 22:33 ` Jonathan Nieder
2014-01-23 20:18 ` Jonathan Nieder
2014-01-23 21:20 ` [PATCH v2 0/3] unaligned reads from .bitmap files Jeff King
2014-01-23 21:23 ` [PATCH 1/3] block-sha1: factor out get_be and put_be wrappers Jeff King
2014-01-23 23:19 ` Jonathan Nieder
2014-01-23 21:26 ` [PATCH 2/3] read-cache: use get_be32 instead of hand-rolled ntoh_l Jeff King
2014-01-23 23:34 ` Jonathan Nieder
2014-01-24 2:22 ` Jeff King
2014-01-23 21:27 ` [PATCH 3/3] ewah: support platforms that require aligned reads Jeff King
2014-01-23 23:44 ` Jonathan Nieder
2014-01-23 23:49 ` Vicent Martí
2014-01-24 0:15 ` Jonathan Nieder
2014-01-23 23:17 ` [PATCH v2 0/3] unaligned reads from .bitmap files Jonathan Nieder
2013-12-21 13:59 ` [PATCH v4 09/23] documentation: add documentation for the bitmap format Jeff King
2013-12-21 14:00 ` [PATCH v4 10/23] pack-bitmap: add support for bitmap indexes Jeff King
2013-12-21 14:00 ` [PATCH v4 11/23] pack-objects: split add_object_entry Jeff King
2013-12-21 14:00 ` [PATCH v4 12/23] pack-objects: use bitmaps when packing objects Jeff King
2013-12-21 14:00 ` [PATCH v4 13/23] rev-list: add bitmap mode to speed up object lists Jeff King
2013-12-21 14:00 ` [PATCH v4 14/23] pack-objects: implement bitmap writing Jeff King
2013-12-21 14:00 ` [PATCH v4 15/23] repack: stop using magic number for ARRAY_SIZE(exts) Jeff King
2013-12-21 14:00 ` [PATCH v4 16/23] repack: turn exts array into array-of-struct Jeff King
2013-12-21 14:00 ` [PATCH v4 17/23] repack: handle optional files created by pack-objects Jeff King
2013-12-21 14:00 ` [PATCH v4 18/23] repack: consider bitmaps when performing repacks Jeff King
2013-12-21 14:00 ` [PATCH v4 19/23] count-objects: recognize .bitmap in garbage-checking Jeff King
2013-12-21 14:00 ` [PATCH v4 20/23] t: add basic bitmap functionality tests Jeff King
2013-12-21 14:00 ` [PATCH v4 21/23] t/perf: add tests for pack bitmaps Jeff King
2013-12-21 14:00 ` [PATCH v4 22/23] pack-bitmap: implement optional name_hash cache Jeff King
2013-12-21 14:00 ` [PATCH v4 23/23] compat/mingw.h: Fix the MinGW and msvc builds Jeff King
2013-12-25 22:08 ` Erik Faye-Lund
2013-12-28 10:00 ` Jeff King
2013-12-28 10:06 ` Vicent Martí
2013-12-28 15:58 ` Ramsay Jones
2013-12-21 14:03 ` [PATCH v4 0/22] pack bitmaps Jeff King
2013-12-21 14:05 ` Jeff King
2013-12-21 18:34 ` Thomas Rast
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