Re: [PATCH v4 08/23] ewah: compressed bitmap implementation

On Thu, Jan 23, 2014 at 12:14:03PM -0800, Shawn Pearce wrote:

quoted

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.

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.

-Peff