Switch to CRC-32C in WAL and other places.

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.

1 files changed, 6 insertions, 6 deletions

diff --git a/src/backend/utils/adt/tsquery.c b/src/backend/utils/adt/tsquery.c
index c8011a8ea92..5226bae2d17 100644
--- a/src/backend/utils/adt/tsquery.c
+++ b/src/backend/utils/adt/tsquery.c
@@ -280,9 +280,9 @@ pushValue(TSQueryParserState state, char *strval, int lenval, int16 weight, bool
 				 errmsg("word is too long in tsquery: \"%s\"",
 						state->buffer)));
 
-	INIT_CRC32(valcrc);
-	COMP_CRC32(valcrc, strval, lenval);
-	FIN_CRC32(valcrc);
+	INIT_LEGACY_CRC32(valcrc);
+	COMP_LEGACY_CRC32(valcrc, strval, lenval);
+	FIN_LEGACY_CRC32(valcrc);
 	pushValue_internal(state, valcrc, state->curop - state->op, lenval, weight, prefix);
 
 	/* append the value string to state.op, enlarging buffer if needed first */
@@ -883,9 +883,9 @@ tsqueryrecv(PG_FUNCTION_ARGS)
 
 			/* Looks valid. */
 
-			INIT_CRC32(valcrc);
-			COMP_CRC32(valcrc, val, val_len);
-			FIN_CRC32(valcrc);
+			INIT_LEGACY_CRC32(valcrc);
+			COMP_LEGACY_CRC32(valcrc, val, val_len);
+			FIN_LEGACY_CRC32(valcrc);
 
 			item->qoperand.weight = weight;
 			item->qoperand.prefix = (prefix) ? true : false;