From: Shawn Pearce <spearce@spearce.org>
Date: Thu, 23 Jan 2014 20:14:03 GMT
Subject: Re: [PATCH v4 08/23] ewah: compressed bitmap implementation
Message-ID: <CAJo=hJtQG_u4=SjPAgU8h4Wew9LjaXUxnHqTT3Q9E1=_5LJ6Sw@mail.gmail.com>
In-Reply-To: <20140123183320.GA22995@sigill.intra.peff.net>

On Thu, Jan 23, 2014 at 10:33 AM, Jeff King <peff@peff.net> wrote:
> On Wed, Jan 22, 2014 at 06:05:36PM -0800, Jonathan Nieder wrote:
>
>> Jeff King wrote:
>>
>> > EWAH is a word-aligned compressed variant of a bitset (i.e. a data
>> > structure that acts as a 0-indexed boolean array for many entries).
>>
>> I suspect that for some callers it's not word-aligned.
>
> Yes, the mmap'd buffers aren't necessarily word-aligned. I don't think
> we can fix that easily without changing the on-disk format (which comes
> from JGit anyway).

Ouch, sorry about that. JGit doesn't mmap the file so we didn't think
about the impact of words not being aligned. I should have caught
that, but I didn't.