#28982 [Opn->Bgs]: rand()%4 is cyclical
| From: | moriyoshi@php.net | Date: | Wed, 14 Jul 2004 17:21:24 +0000 |
| Subject: | #28982 [Opn->Bgs]: rand()%4 is cyclical | ||
| References: | 1 | Groups: | php.bugs |
| Request: | Send a blank email to php-bugs+get-62270@lists.php.net to get a copy of this message | ||
ID: 28982
Updated by: moriyoshi@php.net
Reported By: chsnick at yahoo dot com
-Status: Open
+Status: Bogus
Bug Type: Math related
Operating System: Windows XP
PHP Version: 5.0.0RC3
New Comment:
Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to
report
a bug at http://bugs.php.net/how-to-report.php
See: http://www.eskimo.com/~scs/C-faq/q13.18.html
The tip is of C language, but PHP calls the rand()
library function to generate random values, so it
applies to PHP as well.
Use mt_rand() and you might get better results.
Previous Comments:
------------------------------------------------------------------------
[2004-07-01 08:05:30] chsnick at yahoo dot com
Description:
------------
rand()%4 is cyclical. It proceeds from 0 to 1 to 2 to 3 to 0 to 1,
etc.
Reproduce code:
---------------
srand(5);
for($i = 0; $i < 30; $i++)
{
$j = rand();
$k = $j%4;
echo "$k:$j<br>\n";
}
Actual result:
--------------
2:14426
3:6795
0:22376
1:6017
2:38
3:21607
0:532
1:10941
2:30898
3:20483
0:11136
1:13753
2:28158
3:26975
0:32684
1:29813
2:27658
3:15483
0:27288
1:25329
2:16086
3:9559
0:6212
1:15661
2:29282
3:16371
0:29872
1:32553
2:21166
3:26703
------------------------------------------------------------------------
--
Edit this bug report at http://bugs.php.net/?id=28982&edit=1