note 49237 deleted from function.mt-srand by googleguy
| From: | googleguy@php.net | Date: | Tue, 22 Oct 2013 10:14:14 +0000 |
| Subject: | note 49237 deleted from function.mt-srand by googleguy | ||
| References: | 1 | Groups: | php.notes |
| Request: | Send a blank email to php-notes+get-196922@lists.php.net to get a copy of this message | ||
Note Submitter: Schrecktech
----
::: My seeding report :::
For FreeBSD 4.8-STABLE PHP 4.3.10 it was good enough and faster to not seed at all...although I did
not test the random pseudo terminal.
In detail only seeding once by a previous seed using the hex version (case 3 below) for larger
numbers and longer run times faired the best. For small numbers it was better to not seed at all
(let alone faster). Play with the $loop and $max numbers to see...
<?
function get_a_good_seed
(
$choice = 3
)
{
static $seed;
$seed = 0;
switch($choice)
{
case 1:
// from php.net documentation.
list($usec, $sec) = explode(' ', microtime());
$seed = (float) $sec + ((float) $usec * 1000000);
break;
case 2:
// from high primary number.
$seed = (double)microtime()*1000003;
break;
case 3:
// from a good random source.
$seed = hexdec(substr(md5(microtime()), -8)) & 0x7fffffff;
break;
case 4:
// from random terminal
// NOT TESTED
break;
default:
break;
}
return($seed);
}
function load_last_random
(
)
{
static $last;
static $handle;
// NOTE: create this file with a random integer...
$handle = fopen("random.txt", "r");
while (!feof($handle)) {
$last = fgets($handle, 4096);
}
fclose($handle);
return($last);
}
function save_last_random
(
$save = 0
)
{
$handle = fopen("random.txt", "w");
fwrite($handle, $save);
fclose($handle);
}
function seed_random_number_generator
(
$type = 3,
$ignore_generated_already = FALSE
)
{
static $generator_seeded = FALSE;
if($ignore_generated_already || !$generator_seeded)
{
// 1) load last with time...force integer.
// 2) generate a new random seed and save for next time...
mt_srand(( load_last_random()+get_a_good_seed($type) ) & 0x7fffffff);
save_last_random(mt_rand());
$generator_seeded= TRUE;
}
}
?>