On Thu, Jan 23, 2014 at 02:17:55PM -0800, Jonathan Nieder wrote: > Jeff King wrote: > > On Thu, Jan 23, 2014 at 09:53:26PM +0000, brian m. carlson wrote: > > >> 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 > > I don't think that's a big issue. A pair of 4-byte reads would not be > too slow.
The header is actually two separate 4-byte values, so that's fine. But between the header and trailer are a series of 8-byte data values, and that is what we need the 8-byte alignment for. So the _first_ ewah's data is 8-byte aligned, but then it offsets the alignment with a single 4-byte trailer. So the next ewah, if they are packed in a sequence, is will have its data misaligned. You could solve it by putting an empty 4-byte pad at the end of each ewah (and of course making sure the first one is 8-byte aligned). Anyway, this is all academic until we are designing bitmap v2, which I do not plan on doing anytime soon. -Peff -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
