On 1/9/18 00:17, Michael Paquier wrote: >> * When a type narrower than Datum is stored in a Datum, we place it in the >> * low-order bits and are careful that the DatumGetXXX macro for it discards >> * the unused high-order bits (as opposed to, say, assuming they are zero). >> * This is needed to support old-style user-defined functions, since >> depending >> * on architecture and compiler, the return value of a function returning >> char >> * or short may contain garbage when called as if it returned Datum. >> >> Since we flushed support for V0 functions, the stated rationale doesn't >> apply anymore. I wonder whether there is anything to be gained by >> changing DatumGetXXX and XXXGetDatum to be simple casts (as, if memory >> serves, they once were until we noticed the stated hazard). Or, if >> there's still a reason to keep the masking steps in place, we'd better >> update this comment.
Yeah, we should remove those bit-masking calls if they are no longer necessary. Looking around where else they are used, the uses in numeric.c sure seem like noops: #if SIZEOF_DATUM == 8 #define NumericAbbrevGetDatum(X) ((Datum) SET_8_BYTES(X)) #define DatumGetNumericAbbrev(X) ((int64) GET_8_BYTES(X)) #define NUMERIC_ABBREV_NAN NumericAbbrevGetDatum(PG_INT64_MIN) #else #define NumericAbbrevGetDatum(X) ((Datum) SET_4_BYTES(X)) #define DatumGetNumericAbbrev(X) ((int32) GET_4_BYTES(X)) #define NUMERIC_ABBREV_NAN NumericAbbrevGetDatum(PG_INT32_MIN) #endif We can just replace these by straight casts, too. That leaves the uses in rowtypes.c. Those were introduced as a portability fix by commit 4cbb646334b. I'm curious why these are necessary. The Datums they operate come from heap_deform_tuple(), which gets them from fetchatt(), which does run all pass-by-value values through the very same GET_X_BYTES() macros (until now). I don't see where those dirty upper bits would be coming from. -- Peter Eisentraut http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
