On Sun, Feb 23, 2020 at 04:57:59PM -0500, Jeff King wrote: > It would be nice to get rid of [nth_packed_object_sha1] entirely. In most cases, > it's either free to do so (we end up copying the result into an oid > anyway) or we pay for one extra hashcpy (out of the mmap into a local > struct). But the one in pack-check.c:verify_packfile() is tricky; we > store a pointer per object into the index mmap, and we'd have to switch > to storing an oid per object. Given that the code isn't commonly run > (and other operations like _generating_ the index in the first place are > clearly OK with the extra memory hit), I think I'd be OK with that in > the name of cleanliness. > > All of that is sort of orthogonal to your goals, I think, so I don't > mind at all calling it out of scope for your series. As long as we use > the_hash_algo->rawsz, these bare pointer accesses aren't wrong (it's > just that it's easy to accidentally get it wrong, as this code shows). I looked into this a bit further. It turns out that the current code in verify_packfile() was explicitly trying to avoid that extra memory. But the good news is that I think we can improve it further, cleaning up the existing type-punning and using even less memory than now. I'll prepare a separate series to do that. I had thought the cleanup might also make this whole 20 / the_hash_algo->rawsz thing go away, but it doesn't (the name hashwrite() made me think we ought to be using an oidwrite(), but of course that's silly; the "hash" here is a "file with a hash checksum" and not "an object id hash"). So the two topics really are independent. -Peff
