Update C comments to mention SQL:2003 handling of power return values.

src/backend/utils/adt/float.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/float.c,v 1.155 2008/04/21 00:26:45 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/float.c,v 1.156 2008/05/09 15:36:06 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1331,7 +1331,8 @@ dpow(PG_FUNCTION_ARGS)
 
 	/*
 	 * The SQL spec requires that we emit a particular SQLSTATE error code for
-	 * certain error conditions.
+	 * certain error conditions.  Specifically, we don't return a divide-by-zero
+	 * error code for 0 ^ -1.
 	 */
 	if ((arg1 == 0 && arg2 < 0) ||
 		(arg1 < 0 && floor(arg2) != arg2))

src/backend/utils/adt/numeric.c

@@ -14,7 +14,7 @@
  * Copyright (c) 1998-2008, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/numeric.c,v 1.112 2008/05/08 22:17:54 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/numeric.c,v 1.113 2008/05/09 15:36:06 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1893,8 +1893,9 @@ numeric_power(PG_FUNCTION_ARGS)
 	trunc_var(&arg2_trunc, 0);
 
 	/*
-	 * Return special SQLSTATE error codes for a few conditions mandated by
-	 * the standard.
+	 * The SQL spec requires that we emit a particular SQLSTATE error code for
+	 * certain error conditions.  Specifically, we don't return a divide-by-zero
+	 * error code for 0 ^ -1.
 	 */
 	if ((cmp_var(&arg1, &const_zero) == 0 &&
 		 cmp_var(&arg2, &const_zero) < 0) ||
@@ -5283,6 +5284,7 @@ power_var_int(NumericVar *base, int exp, NumericVar *result, int rscale)
 			/*
 			 *	While 0 ^ 0 can be either 1 or indeterminate (error), we
 			 *	treat it as 1 because most programming languages do this.
+			 *	SQL:2003 also requires a return value of 1.
 			 *	http://en.wikipedia.org/wiki/Exponentiation#Zero_to_the_zero_power
 			 */
 			set_var_from_var(&const_one, result);