Re: What exactly is our CRC algorithm?

On 01/09/2015 10:32 AM, Abhijit Menon-Sen wrote:
> 1. The slicing-by-8 patch contains numerous changes:

With this patch, CALC_CRC32C is no longer a pure macro, but includes a 
function call. That means that you can no longer just #include pg_crc.h 
and pg_crc_tables.h in an external program. We made that arrangement 
with two header files in 2012 [1], and added src/port/pg_crc.c which 
just #includes pg_crc_tables.h, so that the backend and frontend 
programs that use libpgport will have just one copy of the tables.

Now that there's some actual code in pg_crc.c, I think we have to just 
give up on being able to get the CRC implementation without libpgport. 
It was a nice thought, but I doubt there are any programs out there that 
would have a problem with that. Anything that wants to read the WAL 
needs xlogreader.c anyway.

But actually, we should now move pg_crc.c to src/common. It was a bit of 
a hack to have it in src/port in the first place, because it has nothing 
to do with portability, but src/common didn't exist back then. Now it does.

So I propose to move pg_crc.c to src/common, and move the tables from 
pg_crc_tables.h directly to pg_crc.c. Thoughts?

[1] 
http://www.postgresql.org/message-id/flat/CAAZKuFaNcf3=YtadkWwr8yHb+1axW2RepmQ2j8a9NNGkV7PN=w@mail.gmail.com.

- Heikki