Document and enforce that the usable range of setseed() arguments is

-1 to 1, not 0 to 1.  The actual behavior for values within this range
does not change.  Kris Jurka

doc/src/sgml/func.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.423 2008/03/06 18:49:32 momjian Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.424 2008/03/10 12:39:22 tgl Exp $ -->
 
  <chapter id="functions">
   <title>Functions and Operators</title>
@@ -828,7 +828,7 @@
       <row>
        <entry><literal><function>setseed</function>(<type>dp</type>)</literal></entry>
        <entry><type>void</type></entry>
-       <entry>set seed for subsequent <literal>random()</literal> calls (value between 0 and 1.0)</entry>
+       <entry>set seed for subsequent <literal>random()</literal> calls (value between -1.0 and 1.0)</entry>
        <entry><literal>setseed(0.54823)</literal></entry>
        <entry></entry>
       </row>

doc/src/sgml/ref/set.sgml

 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/set.sgml,v 1.91 2007/09/11 00:06:41 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/set.sgml,v 1.92 2008/03/10 12:39:22 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -166,7 +166,7 @@ SET [ SESSION | LOCAL ] TIME ZONE { <replaceable class="PARAMETER">timezone</rep
       <para>
        Sets the internal seed for the random number generator (the
        function <function>random</function>).  Allowed values are
-       floating-point numbers between 0 and 1, which are then
+       floating-point numbers between -1 and 1, which are then
        multiplied by 2<superscript>31</>-1.
       </para>
 

src/backend/utils/adt/float.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/float.c,v 1.153 2008/01/01 19:45:52 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/float.c,v 1.154 2008/03/10 12:39:22 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1684,8 +1684,12 @@ Datum
 setseed(PG_FUNCTION_ARGS)
 {
 	float8		seed = PG_GETARG_FLOAT8(0);
-	int			iseed = (int) (seed * MAX_RANDOM_VALUE);
+	int			iseed;
 
+	if (seed < -1 || seed > 1)
+		elog(ERROR, "setseed parameter %f out of range [-1,1]", seed);
+
+	iseed = (int) (seed * MAX_RANDOM_VALUE);
 	srandom((unsigned int) iseed);
 
 	PG_RETURN_VOID();

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 1.435 2008/03/10 03:22:29 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.436 2008/03/10 12:39:23 tgl Exp $
  *
  *--------------------------------------------------------------------
  */
@@ -1849,7 +1849,7 @@ static struct config_real ConfigureNamesReal[] =
 			GUC_NO_SHOW_ALL | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
 		&phony_random_seed,
-		0.5, 0.0, 1.0, assign_random_seed, show_random_seed
+		0.0, -1.0, 1.0, assign_random_seed, show_random_seed
 	},
 
 	{