Clean up problems with rounding/overflow code in NUMERIC, particularly

the case wherein zero was rejected for a field like NUMERIC(4,4).
Miscellaneous other code beautification efforts.

src/include/utils/numeric.h

@@ -5,7 +5,7 @@
  *
  *	1998 Jan Wieck
  *
- * $Header: /cvsroot/pgsql/src/include/utils/numeric.h,v 1.7 1999/07/14 01:20:30 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/include/utils/numeric.h,v 1.8 2000/01/15 23:42:48 tgl Exp $
  *
  * ----------
  */
@@ -21,31 +21,41 @@
 #define NUMERIC_DEFAULT_PRECISION	30
 #define NUMERIC_DEFAULT_SCALE		6
 
+
+/* ----------
+ * Internal limits on the scales chosen for calculation results
+ * ----------
+ */
 #define NUMERIC_MAX_DISPLAY_SCALE	NUMERIC_MAX_PRECISION
-#define NUMERIC_MIN_DISPLAY_SCALE	NUMERIC_DEFAULT_SCALE + 4
+#define NUMERIC_MIN_DISPLAY_SCALE	(NUMERIC_DEFAULT_SCALE + 4)
 
 #define NUMERIC_MAX_RESULT_SCALE	(NUMERIC_MAX_PRECISION * 2)
 #define NUMERIC_MIN_RESULT_SCALE	(NUMERIC_DEFAULT_PRECISION + 4)
 
-#define NUMERIC_UNPACKED_DATASIZE	(NUMERIC_MAX_PRECISION * 2 + 4)
-
 
 /* ----------
- * Sign values and macros to deal with n_sign_dscale
+ * Sign values and macros to deal with packing/unpacking n_sign_dscale
  * ----------
  */
 #define NUMERIC_SIGN_MASK	0xC000
 #define NUMERIC_POS			0x0000
 #define NUMERIC_NEG			0x4000
 #define NUMERIC_NAN			0xC000
+#define NUMERIC_DSCALE_MASK	0x3FFF
 #define NUMERIC_SIGN(n)		((n)->n_sign_dscale & NUMERIC_SIGN_MASK)
-#define NUMERIC_DSCALE(n)	((n)->n_sign_dscale & ~NUMERIC_SIGN_MASK)
+#define NUMERIC_DSCALE(n)	((n)->n_sign_dscale & NUMERIC_DSCALE_MASK)
 #define NUMERIC_IS_NAN(n)	(NUMERIC_SIGN(n) != NUMERIC_POS &&			\
 								NUMERIC_SIGN(n) != NUMERIC_NEG)
 
 
 /* ----------
  * The Numeric data type stored in the database
+ *
+ * NOTE: by convention, values in the packed form have been stripped of
+ * all leading and trailing zeroes (except there will be a trailing zero
+ * in the last byte, if the number of digits is odd).  In particular,
+ * if the value is zero, there will be no digits at all!  The weight is
+ * arbitrary in this case, but we normally set it to zero.
  * ----------
  */
 typedef struct NumericData
@@ -54,7 +64,7 @@ typedef struct NumericData
 	int16		n_weight;		/* Weight of 1st digit	*/
 	uint16		n_rscale;		/* Result scale			*/
 	uint16		n_sign_dscale;	/* Sign + display scale */
-	unsigned char n_data[1];	/* Digit data			*/
+	unsigned char n_data[1];	/* Digit data (2 decimal digits/byte) */
 } NumericData;
 typedef NumericData *Numeric;