Increase the maximum value of extra_float_digits to 3, and have pg_dump

use that value when the backend is new enough to allow it.  This responds
to bug report from Keh-Cheng Chu pointing out that although 2 extra digits
should be sufficient to dump and restore float8 exactly, it is possible to
need 3 extra digits for float4 values.

doc/src/sgml/config.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.226 2009/09/10 15:02:46 alvherre Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.227 2009/09/11 19:17:03 tgl Exp $ -->
 
 <chapter Id="runtime-config">
   <title>Server Configuration</title>
@@ -4291,7 +4291,7 @@ SET XML OPTION { DOCUMENT | CONTENT };
         floating-point values, including <type>float4</>, <type>float8</>,
         and geometric data types.  The parameter value is added to the
         standard number of digits (<literal>FLT_DIG</> or <literal>DBL_DIG</>
-        as appropriate).  The value can be set as high as 2, to include
+        as appropriate).  The value can be set as high as 3, to include
         partially-significant digits; this is especially useful for dumping
         float data that needs to be restored exactly.  Or it can be set
         negative to suppress unwanted digits.

src/backend/utils/adt/float.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/float.c,v 1.162 2009/06/11 14:49:03 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/float.c,v 1.163 2009/09/11 19:17:03 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -334,7 +334,7 @@ float4out(PG_FUNCTION_ARGS)
 				if (ndig < 1)
 					ndig = 1;
 
-				sprintf(ascii, "%.*g", ndig, num);
+				snprintf(ascii, MAXFLOATWIDTH + 1, "%.*g", ndig, num);
 			}
 	}
 
@@ -523,7 +523,7 @@ float8out(PG_FUNCTION_ARGS)
 				if (ndig < 1)
 					ndig = 1;
 
-				sprintf(ascii, "%.*g", ndig, num);
+				snprintf(ascii, MAXDOUBLEWIDTH + 1, "%.*g", ndig, num);
 			}
 	}
 

src/backend/utils/adt/geo_ops.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/geo_ops.c,v 1.104 2009/08/27 15:59:22 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/geo_ops.c,v 1.105 2009/09/11 19:17:03 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -85,8 +85,8 @@ static Point* lseg_interpt_internal(LSEG *l1, LSEG *l2);
 #define RDELIM_C		'>'
 
 /* Maximum number of characters printed by pair_encode() */
-/* ...+2+7 : 2 accounts for extra_float_digits max value */
-#define P_MAXLEN (2*(DBL_DIG+2+7)+1)
+/* ...+3+7 : 3 accounts for extra_float_digits max value */
+#define P_MAXLEN (2*(DBL_DIG+3+7)+1)
 
 
 /*

src/backend/utils/misc/guc.c

@@ -10,7 +10,7 @@
  * Written by Peter Eisentraut <peter_e@gmx.net>.
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.516 2009/09/08 17:08:36 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.517 2009/09/11 19:17:03 tgl Exp $
  *
  *--------------------------------------------------------------------
  */
@@ -1684,7 +1684,7 @@ static struct config_int ConfigureNamesInt[] =
 						 "(FLT_DIG or DBL_DIG as appropriate).")
 		},
 		&extra_float_digits,
-		0, -15, 2, NULL, NULL
+		0, -15, 3, NULL, NULL
 	},
 
 	{

src/backend/utils/misc/postgresql.conf.sample

@@ -445,7 +445,7 @@
 					#   India
 					# You can create your own file in
 					# share/timezonesets/.
-#extra_float_digits = 0			# min -15, max 2
+#extra_float_digits = 0			# min -15, max 3
 #client_encoding = sql_ascii		# actually, defaults to database
 					# encoding
 

src/bin/pg_dump/pg_dump.c

@@ -12,7 +12,7 @@
  *	by PostgreSQL
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/bin/pg_dump/pg_dump.c,v 1.546 2009/08/04 19:46:51 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/bin/pg_dump/pg_dump.c,v 1.547 2009/09/11 19:17:04 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -595,7 +595,9 @@ main(int argc, char **argv)
 	 * If supported, set extra_float_digits so that we can dump float data
 	 * exactly (given correctly implemented float I/O code, anyway)
 	 */
-	if (g_fout->remoteVersion >= 70400)
+	if (g_fout->remoteVersion >= 80500)
+		do_sql_command(g_conn, "SET extra_float_digits TO 3");
+	else if (g_fout->remoteVersion >= 70400)
 		do_sql_command(g_conn, "SET extra_float_digits TO 2");
 
 	/*