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.

diff --git a/contrib/pgbench/pgbench.c b/contrib/pgbench/pgbench.c
index ce35bd3dff57a1fae98731550b6787c1c01356bd..b5082e0abd62efb9d1a7e68eb7b1d1e149ce5713 100644 (file)
--- 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 */