<entry>convert floating point to integer</entry>
<entry>integer(2.0)</entry>
</row>
+ <row>
+ <entry>random()</entry>
+ <entry>float8</entry>
+ <entry>random value in the range 0.0 to 1.0</entry>
+ <entry>random()</entry>
+ </row>
+ <row>
+ <entry>setseed(float8)</entry>
+ <entry>int</entry>
+ <entry>set seed for subsequent random() calls</entry>
+ <entry>setseed(0.54823)</entry>
+ </row>
</tbody>
</tgroup>
</table>
<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/ref/set.sgml,v 1.46 2000/07/14 15:27:14 thomas Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/ref/set.sgml,v 1.47 2000/08/07 00:51:18 tgl Exp $
Postgres documentation
-->
<listitem>
<para>
The value for the seed to be used by the
- <function>random</function> catalog function. Significant
+ <function>random</function> function. Allowed
values are floating point numbers between 0 and 1, which
- are then multiplied by RAND_MAX. This product will
+ are then multiplied by 2^31-1. This product will
silently overflow if a number outside the range is used.
</para>
* Portions Copyright (c) 1996-2000, PostgreSQL, Inc
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $Id: geqo_main.c,v 1.22 2000/06/28 03:31:45 tgl Exp $
+ * $Id: geqo_main.c,v 1.23 2000/08/07 00:51:23 tgl Exp $
*
*-------------------------------------------------------------------------
*/
/* seed random number generator */
/* XXX why is this done every time around? */
if (Geqo_random_seed >= 0)
- srandom(Geqo_random_seed);
+ srandom((unsigned int) Geqo_random_seed);
else
- srandom(time(NULL));
+ srandom((unsigned int) time(NULL));
/* allocate genetic pool memory */
pool = alloc_pool(pool_size, number_of_rels);
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/postmaster/postmaster.c,v 1.158 2000/07/28 02:13:26 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/postmaster/postmaster.c,v 1.159 2000/08/07 00:51:30 tgl Exp $
*
* NOTES
*
*/
random_seed = 0;
gettimeofday(&now, &tz);
- srandom(now.tv_usec);
+ srandom((unsigned int) now.tv_usec);
/* ----------------
* Now, build the argv vector that will be given to PostgresMain.
static long
PostmasterRandom(void)
{
-
static bool initialized = false;
if (!initialized)
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/utils/adt/float.c,v 1.67 2000/08/01 18:29:35 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/utils/adt/float.c,v 1.68 2000/08/07 00:51:14 tgl Exp $
*
*-------------------------------------------------------------------------
*/
float8 result;
/* result 0.0-1.0 */
- result = ((double) random()) / RAND_MAX;
+ result = ((double) random()) / ((double) MAX_RANDOM_VALUE);
PG_RETURN_FLOAT8(result);
}
setseed(PG_FUNCTION_ARGS)
{
float8 seed = PG_GETARG_FLOAT8(0);
- int iseed = (seed * RAND_MAX);
+ int iseed = (int) (seed * MAX_RANDOM_VALUE);
srandom((unsigned int) iseed);
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/utils/adt/misc.c,v 1.19 2000/06/05 07:28:52 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/utils/adt/misc.c,v 1.20 2000/08/07 00:51:14 tgl Exp $
*
*-------------------------------------------------------------------------
*/
/*
* oidrand (oid o, int4 X)-
- * takes in an oid and a int4 X, and will return 'true'
- * about 1/X of the time.
+ * Takes in an oid and a int4 X, and will return 'true' about 1/X of
+ * the time. If X == 0, this will always return true.
* Useful for doing random sampling or subsetting.
- * if X == 0, this will always return true;
*
* Example use:
* select * from TEMP where oidrand(TEMP.oid, 10)
* will return about 1/10 of the tuples in TEMP
*
+ * NOTE: the OID input is not used at all. It is there just because of
+ * an old optimizer bug: a qual expression containing no variables was
+ * mistakenly assumed to be a constant. Pretending to access the row's OID
+ * prevented the optimizer from treating the oidrand() result as constant.
*/
static bool random_initialized = false;
Datum
oidrand(PG_FUNCTION_ARGS)
{
- /* XXX seems like we ought to be using the oid for something? */
#ifdef NOT_USED
Oid o = PG_GETARG_OID(0);
#endif
{
int32 X = PG_GETARG_INT32(0);
- srand(X);
+ srandom((unsigned int) X);
random_initialized = true;
PG_RETURN_BOOL(true);
}
* or in config.h afterwards. Of course, if you edit config.h, then your
* changes will be overwritten the next time you run configure.
*
- * $Id: config.h.in,v 1.128 2000/07/28 02:13:40 tgl Exp $
+ * $Id: config.h.in,v 1.129 2000/08/07 00:51:38 tgl Exp $
*/
#ifndef CONFIG_H
extern void srandom(unsigned int seed);
#endif
+/* The random() function is expected to yield values 0 .. MAX_RANDOM_VALUE */
+/* Currently, all known implementations yield 0..2^31-1, so we just hardwire
+ * this constant. We could do a configure test if it proves to be necessary.
+ * CAUTION: Think not to replace this with RAND_MAX. RAND_MAX defines the
+ * maximum value of the older rand() function, which is often different from
+ * --- and considerably inferior to --- random().
+ */
+#define MAX_RANDOM_VALUE (0x7FFFFFFF)
+
/* Set to 1 if you have libz.a */
#undef HAVE_LIBZ
* Portions Copyright (c) 1996-2000, PostgreSQL, Inc
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $Id: geqo_random.h,v 1.6 2000/01/26 05:58:20 momjian Exp $
+ * $Id: geqo_random.h,v 1.7 2000/08/07 00:51:42 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include <math.h>
-#define GEQOMASK 2147483647
+/* geqo_rand returns a random float value between 0 and 1 inclusive */
-#define geqo_rand() ((double)random()/GEQOMASK)
+#define geqo_rand() (((double) random()) / ((double) MAX_RANDOM_VALUE))
-/* geqo_randint returns integer value
- between lower and upper inclusive */
+/* geqo_randint returns integer value between lower and upper inclusive */
-#define geqo_randint(upper,lower) ( (int) floor( geqo_rand()*((upper-lower)+0.999999) ) + lower )
+#define geqo_randint(upper,lower) \
+ ( (int) floor( geqo_rand()*(((upper)-(lower))+0.999999) ) + (lower) )
#endif /* GEQO_RANDOM_H */
projects / thirdparty / postgresql.git / commitdiff
