Tom Lane wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > Because random returns a double, I think it is very possible that we
> > could return 1 due to rounding,
>
> Not unless your machine has a "double" type with less than 32 bits of
> precision, which seems pretty unlikely. It'd be sufficient to do
>
> /* result 0.0 <= x < 1.0 */
> result = ((double) random()) / ((double) MAX_RANDOM_VALUE + 1.0);
Here is a patch that makes this change, and cleans up other
MAX_RANDOM_VALUE uses.
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073
Index: src/backend/commands/analyze.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/commands/analyze.c,v
retrieving revision 1.90
diff -c -c -r1.90 analyze.c
*** src/backend/commands/analyze.c 22 Nov 2005 18:17:08 -0000 1.90
--- src/backend/commands/analyze.c 26 Jan 2006 23:40:49 -0000
***************
*** 927,944 ****
return numrows;
}
! /* Select a random value R uniformly distributed in 0 < R < 1 */
static double
random_fract(void)
{
! long z;
!
! /* random() can produce endpoint values, try again if so */
! do
! {
! z = random();
! } while (z <= 0 || z >= MAX_RANDOM_VALUE);
! return (double) z / (double) MAX_RANDOM_VALUE;
}
/*
--- 927,937 ----
return numrows;
}
! /* Select a random value R uniformly distributed in (0 - 1) */
static double
random_fract(void)
{
! return ((double) random() + 1) / ((double) MAX_RANDOM_VALUE + 2);
}
/*
Index: src/backend/storage/lmgr/s_lock.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/storage/lmgr/s_lock.c,v
retrieving revision 1.41
diff -c -c -r1.41 s_lock.c
*** src/backend/storage/lmgr/s_lock.c 22 Nov 2005 18:17:21 -0000 1.41
--- src/backend/storage/lmgr/s_lock.c 26 Jan 2006 23:40:54 -0000
***************
*** 120,126 ****
/* increase delay by a random fraction between 1X and
2X */
cur_delay += (int) (cur_delay *
! (((double) random()) / ((double)
MAX_RANDOM_VALUE)) + 0.5);
/* wrap back to minimum delay when max is exceeded */
if (cur_delay > MAX_DELAY_MSEC)
cur_delay = MIN_DELAY_MSEC;
--- 120,126 ----
/* increase delay by a random fraction between 1X and
2X */
cur_delay += (int) (cur_delay *
! ((double) random() / (double)
MAX_RANDOM_VALUE) + 0.5);
/* wrap back to minimum delay when max is exceeded */
if (cur_delay > MAX_DELAY_MSEC)
cur_delay = MIN_DELAY_MSEC;
Index: src/backend/utils/adt/float.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/utils/adt/float.c,v
retrieving revision 1.119
diff -c -c -r1.119 float.c
*** src/backend/utils/adt/float.c 2 Dec 2005 02:49:11 -0000 1.119
--- src/backend/utils/adt/float.c 26 Jan 2006 23:40:57 -0000
***************
*** 1833,1840 ****
{
float8 result;
! /* result 0.0-1.0 */
! result = ((double) random()) / ((double) MAX_RANDOM_VALUE);
PG_RETURN_FLOAT8(result);
}
--- 1833,1840 ----
{
float8 result;
! /* result [0.0 - 1.0) */
! result = (double) random() / ((double) MAX_RANDOM_VALUE + 1);
PG_RETURN_FLOAT8(result);
}
Index: src/include/optimizer/geqo_random.h
===================================================================
RCS file: /cvsroot/pgsql/src/include/optimizer/geqo_random.h,v
retrieving revision 1.16
diff -c -c -r1.16 geqo_random.h
*** src/include/optimizer/geqo_random.h 31 Dec 2004 22:03:36 -0000 1.16
--- src/include/optimizer/geqo_random.h 26 Jan 2006 23:40:58 -0000
***************
*** 28,34 ****
/* geqo_rand returns a random float value between 0 and 1 inclusive */
! #define geqo_rand() (((double) random()) / ((double) MAX_RANDOM_VALUE))
/* geqo_randint returns integer value between lower and upper inclusive */
--- 28,34 ----
/* geqo_rand returns a random float value between 0 and 1 inclusive */
! #define geqo_rand() ((double) random() / (double) MAX_RANDOM_VALUE)
/* geqo_randint returns integer value between lower and upper inclusive */
---------------------------(end of broadcast)---------------------------
TIP 6: explain analyze is your friend
