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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2008-03-10 01:23:04 +0000 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2008-03-10 01:23:04 +0000 |
| commit | 9537739f7fcd3bafa2471b199297ec7ad7c935e7 (patch) | |
| tree | 4282364b9527cdbb56bd16d68e21696ae71615da | |
| parent | d9384a4b7334ba755db88160fb96cd33725bd6d3 (diff) | |
| download | postgresql-9537739f7fcd3bafa2471b199297ec7ad7c935e7.tar.gz postgresql-9537739f7fcd3bafa2471b199297ec7ad7c935e7.zip | |
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.
| -rw-r--r-- | contrib/pgbench/pgbench.c | 10 |
1 files 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 */ |