diff options
Diffstat (limited to 'src/include/postgres.h')
| -rw-r--r-- | src/include/postgres.h | 14 |
1 files changed, 10 insertions, 4 deletions
diff --git a/src/include/postgres.h b/src/include/postgres.h index 00c92e7822..719f64ea78 100644 --- a/src/include/postgres.h +++ b/src/include/postgres.h @@ -125,13 +125,18 @@ typedef struct varattrib * * sizeof(short) == 2 * - * If your machine meets these requirements, Datums should also be checked - * to see if the positioning is correct. + * 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. */ typedef unsigned long Datum; /* XXX sizeof(long) >= sizeof(void *) */ #define SIZEOF_DATUM SIZEOF_UNSIGNED_LONG + typedef Datum *DatumPtr; #define GET_1_BYTE(datum) (((Datum) (datum)) & 0x000000ff) @@ -145,10 +150,11 @@ typedef Datum *DatumPtr; * DatumGetBool * Returns boolean value of a datum. * - * Note: any nonzero value will be considered TRUE. + * Note: any nonzero value will be considered TRUE, but we ignore bits to + * the left of the width of bool, per comment above. */ -#define DatumGetBool(X) ((bool) (((Datum) (X)) != 0)) +#define DatumGetBool(X) ((bool) (((bool) (X)) != 0)) /* * BoolGetDatum |