From 9537739f7fcd3bafa2471b199297ec7ad7c935e7 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Mon, 10 Mar 2008 01:23:04 +0000
Subject: [PATCH] Fix pgbench's getrand() function so that min and max have
approximately the same chance of being selected as do numbers between them.
Problem noted by Greg Stark; fix by Alexey Klyukin.
---
contrib/pgbench/pgbench.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/contrib/pgbench/pgbench.c b/contrib/pgbench/pgbench.c
index ce35bd3dff5..b5082e0abd6 100644
--- a/contrib/pgbench/pgbench.c
+++ b/contrib/pgbench/pgbench.c
@@ -1,5 +1,5 @@
/*
- * $PostgreSQL: pgsql/contrib/pgbench/pgbench.c,v 1.75 2007/12/11 02:31:49 tgl Exp $
+ * $PostgreSQL: pgsql/contrib/pgbench/pgbench.c,v 1.76 2008/03/10 01:23:04 tgl Exp $
*
* pgbench: a simple benchmark program for PostgreSQL
* written by Tatsuo Ishii
@@ -191,11 +191,15 @@ usage(void)
fprintf(stderr, "(initialize mode): pgbench -i [-h hostname][-p port][-s scaling_factor] [-F fillfactor] [-U login][-d][dbname]\n");
}
-/* random number generator */
+/* random number generator: uniform distribution from min to max inclusive */
static int
getrand(int min, int max)
{
- return min + (int) (((max - min) * (double) random()) / MAX_RANDOM_VALUE + 0.5);
+ /*
+ * Odd coding is so that min and max have approximately the same chance of
+ * being selected as do numbers between them.
+ */
+ return min + (int) (((max - min + 1) * (double) random()) / (MAX_RANDOM_VALUE + 1.0));
}
/* call PQexec() and exit() on failure */
--
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