On 18.04.2013, at 20:02, Ants Aasma <a...@cybertec.at> wrote: > On Thu, Apr 18, 2013 at 8:24 PM, Ants Aasma <a...@cybertec.at> wrote: >> On Thu, Apr 18, 2013 at 8:15 PM, Florian Pflug <f...@phlo.org> wrote: >>> So either the CRC32-C polynomial isn't irreducible, or there something >>> fishy going on. Could there be a bug in your CRC implementation? Maybe >>> a mixup between big and little endian, or something like that? >> >> I'm suspecting an implementation bug myself. I already checked the >> test harness and that was all sane, compiler hadn't taken any >> unforgivable liberties there. I will crosscheck the output with other >> implementations to verify that the checksum is implemented correctly. > > Looks like the implementation is correct. I cross-referenced it > against a bitwise algorithm for crc32 with the castagnoli polynomial. > This also rules out any endianness issues as the bitwise variant > consumes input byte at a time. > > What ever it is, it is something specific to PostgreSQL page layout. > If I use /dev/urandom as the source the issue disappears. So much for > CRC32 being proven good.
Weird. Is the code of your test harness available publicly, or could you post it? I'd like to look into this... best regard, Florian Pflug -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
