mirror of
https://git.postgresql.org/git/postgresql.git
synced 2024-08-22 08:23:22 +02:00
The old algorithm was found to not be the usual CRC-32 algorithm, used by Ethernet et al. We were using a non-reflected lookup table with code meant for a reflected lookup table. That's a strange combination that AFAICS does not correspond to any bit-wise CRC calculation, which makes it difficult to reason about its properties. Although it has worked well in practice, seems safer to use a well-known algorithm. Since we're changing the algorithm anyway, we might as well choose a different polynomial. The Castagnoli polynomial has better error-correcting properties than the traditional CRC-32 polynomial, even if we had implemented it correctly. Another reason for picking that is that some new CPUs have hardware support for calculating CRC-32C, but not CRC-32, let alone our strange variant of it. This patch doesn't add any support for such hardware, but a future patch could now do that. The old algorithm is kept around for tsquery and pg_trgm, which use the values in indexes that need to remain compatible so that pg_upgrade works. While we're at it, share the old lookup table for CRC-32 calculation between hstore, ltree and core. They all use the same table, so might as well. |
||
---|---|---|
.. | ||
backend | ||
bin | ||
common | ||
include | ||
interfaces | ||
makefiles | ||
pl | ||
port | ||
template | ||
test | ||
timezone | ||
tools | ||
tutorial | ||
.gitignore | ||
bcc32.mak | ||
DEVELOPERS | ||
Makefile | ||
Makefile.global.in | ||
Makefile.shlib | ||
nls-global.mk | ||
win32.mak |