Extend numeric_round and numeric_trunc to accept negative scale inputs

(ie, allow rounding to occur at a digit position left of the decimal
point).  Apparently this is how Oracle handles it, and there are
precedents in other programming languages as well.

diff --git a/src/backend/utils/adt/numeric.c b/src/backend/utils/adt/numeric.c
index a3e9a7d..4d46992 100644 (file)
--- a/src/backend/utils/adt/numeric.c
+++ b/src/backend/utils/adt/numeric.c
@@ -5,7 +5,7 @@
  *
  *     1998 Jan Wieck
  *
- * $Header: /cvsroot/pgsql/src/backend/utils/adt/numeric.c,v 1.25 2000/02/24 02:05:30 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/utils/adt/numeric.c,v 1.26 2000/03/13 02:31:13 tgl Exp $
  *
  * ----------
  */
@@ -491,14 +491,17 @@ numeric_sign(Numeric num)
 /* ----------
  * numeric_round() -
  *
- *     Modify rscale and dscale of a number and round it if required.
+ *     Round a value to have 'scale' digits after the decimal point.
+ *     We allow negative 'scale', implying rounding before the decimal
+ *     point --- Oracle interprets rounding that way.
  * ----------
  */
 Numeric
 numeric_round(Numeric num, int32 scale)
 {
-       int32           typmod;
-       int                     precision;
+       Numeric         res;
+       NumericVar      arg;
+       int                     i;
 
        /* ----------
         * Handle NULL
@@ -515,27 +518,79 @@ numeric_round(Numeric num, int32 scale)
                return make_result(&const_nan);
 
        /* ----------
-        * Check that the requested scale is valid
+        * Limit the scale value to avoid possible overflow in calculations below.
         * ----------
         */
-       if (scale < 0 || scale > NUMERIC_MAX_DISPLAY_SCALE)
-               elog(ERROR, "illegal numeric scale %d - must be between 0 and %d",
-                        scale, NUMERIC_MAX_DISPLAY_SCALE);
+       scale = MIN(NUMERIC_MAX_RESULT_SCALE,
+                               MAX(-NUMERIC_MAX_RESULT_SCALE, scale));
 
        /* ----------
-        * Let numeric() and in turn apply_typmod() do the job
+        * Unpack the argument and round it at the proper digit position
         * ----------
         */
-       precision = MAX(0, num->n_weight) + scale;
-       typmod = (((precision + 2) << 16) | scale) + VARHDRSZ;
-       return numeric(num, typmod);
+       init_var(&arg);
+       set_var_from_num(num, &arg);
+
+       i = arg.weight + scale + 1;
+
+       if (i < arg.ndigits)
+       {
+               /* If i = 0, the value loses all digits, but could round up if its
+                * first digit is more than 4.  If i < 0 the result must be 0.
+                */
+               if (i < 0)
+               {
+                       arg.ndigits = 0;
+               }
+               else
+               {
+                       int             carry = (arg.digits[i] > 4) ? 1 : 0;
+
+                       arg.ndigits = i;
+
+                       while (carry)
+                       {
+                               carry += arg.digits[--i];
+                               arg.digits[i] = carry % 10;
+                               carry /= 10;
+                       }
+
+                       if (i < 0)
+                       {
+                               Assert(i == -1); /* better not have added more than 1 digit */
+                               Assert(arg.digits > arg.buf);
+                               arg.digits--;
+                               arg.ndigits++;
+                               arg.weight++;
+                       }
+               }
+       }
+
+       /* ----------
+        * Set result's scale to something reasonable.
+        * ----------
+        */
+       scale = MIN(NUMERIC_MAX_DISPLAY_SCALE, MAX(0, scale));
+       arg.rscale = scale;
+       arg.dscale = scale;
+
+       /* ----------
+        * Return the rounded result
+        * ----------
+        */
+       res = make_result(&arg);
+
+       free_var(&arg);
+       return res;
 }
 
 
 /* ----------
  * numeric_trunc() -
  *
- *     Modify rscale and dscale of a number and cut it if required.
+ *     Truncate a value to have 'scale' digits after the decimal point.
+ *     We allow negative 'scale', implying a truncation before the decimal
+ *     point --- Oracle interprets truncation that way.
  * ----------
  */
 Numeric
@@ -559,25 +614,29 @@ numeric_trunc(Numeric num, int32 scale)
                return make_result(&const_nan);
 
        /* ----------
-        * Check that the requested scale is valid
+        * Limit the scale value to avoid possible overflow in calculations below.
         * ----------
         */
-       if (scale < 0 || scale > NUMERIC_MAX_DISPLAY_SCALE)
-               elog(ERROR, "illegal numeric scale %d - must be between 0 and %d",
-                        scale, NUMERIC_MAX_DISPLAY_SCALE);
+       scale = MIN(NUMERIC_MAX_RESULT_SCALE,
+                               MAX(-NUMERIC_MAX_RESULT_SCALE, scale));
 
        /* ----------
-        * Unpack the argument and truncate it
+        * Unpack the argument and truncate it at the proper digit position
         * ----------
         */
        init_var(&arg);
        set_var_from_num(num, &arg);
 
+       arg.ndigits = MIN(arg.ndigits, MAX(0, arg.weight + scale + 1));
+
+       /* ----------
+        * Set result's scale to something reasonable.
+        * ----------
+        */
+       scale = MIN(NUMERIC_MAX_DISPLAY_SCALE, MAX(0, scale));
        arg.rscale = scale;
        arg.dscale = scale;
 
-       arg.ndigits = MIN(arg.ndigits, MAX(0, arg.weight + scale + 1));
-
        /* ----------
         * Return the truncated result
         * ----------