Re: [RFC PATCH 10/10] pack-objects: improve partial packfile reuse

[Jeff King <peff@peff.net>]

On Thu, Oct 17, 2019 at 04:03:00PM +0900, Junio C Hamano wrote:

> Jeff King <peff@peff.net> writes:
> 
> >> Hmm, I am kind of surprised that the decoding side allowed such a
> >> padding.
> >
> > IIRC, the "padding" is just a sequence of 0-length-plus-continuation-bit
> > varint bytes. And for some reason it worked for the size but not for the
> > delta offset value.
> 
> I think the reason is because they use different varint definition.
> 
> The encoding used in builtin/pack-objects.c::write_no_reuse_object()
> is for offsets, and it came much later and with an improvement over
> the encoding used for delta size in diff-delta.c::create_delta().
> The more recent encoding does not allow padding (when I compare the
> decoders for these two encodings, I notice there is +1 for each
> 7-bit iteration; this essentially declares that a byte with "not the
> final byte" bit set with all other bits clear does not mean 0 but it
> means 1, which breaks the idea of padding to encode filler zero
> bits).

Yeah, that sounds right. I think the "old" one is actually the pack size
header in unpack_object_header_buffer(), not the delta size header.

At any rate, it seems like a terrible idea, so I'll be glad to see the
code dropped. :)

-Peff