Re: What exactly is our CRC algorithm?

Hi Heikki.

I've attached two regenerated CRC patches, split up as before.

1. The slicing-by-8 patch contains numerous changes:

    a. A configure test for __builtin_bswap32
    b. A comment referencing the slicing-by-8 paper (which is behind a
       paywall, unfortunately, so I haven't even read it). Are more
       comments needed? If so, where/what kind?
    c. A byte-reversed big-endian version of the 8*256 table. In Linux,
       there's only one table that uses __constant_swab32, but for us
       it's simpler to have two tables.
    d. Thanks to (c), we can avoid the bswap32 in the hot loop.
    e. On big-endian systems, FIN_CRC32C now bswap32()s the CRC before
       finalising it. (We don't need to do this in INIT_CRC32C only
       because the initialiser is 0xFFFFFFFF.)

2. The sse4.2 patch has only some minor compile fixes.

I have built and tested both patches individually on little-endian
(amd64) and big-endian (ppc) systems. I verified that the _sse is
chosen at startup on the former, and _sb8 on the latter, and that
both implementations function correctly with respect to HEAD.

Please let me know if there's anything else I need to do.

-- Abhijit