note 16502 added to function.mt-srand

I see a problem with seeding with: mt_srand((double)microtime()*1000000); Too few seeds. This chooses the seed from a space of only one million seeds. This is a shame, because the Mersenne Twister algorithm has a period of 2**19937-1. So of all the possible starting points in the MT sequence, the above seed only chooses at random from among 1000000 starting points, or about 0.000...0001% of the possible starting points, where "..." is a string of about 5986 more zeros! In real life, this means that if you note the first few random numbers, when you see the same first few numbers again, the chances are very good that you have the same seed and the rest of the sequence will be the same too. If you generate a random "unique" 100-character key for say cookie use, seeding as above, you will likely get a duplicate key after only 1000 keys or so. Better: To supplement the results from mt_rand, also hash in the entire contents of the microtime() string. Better still: Use a 31-bit hash of microtime() as the seed. Problem 2. Way too few seeds on some hardware. It is bad to rely on a clock ticking every microsecond. I have used computers where 100ms was the finest-resolution clock available. That would be just 10 different seeds, as the results from (double)microtime() would look like: 0.10000000 0.20000000 etc. -- http://www.php.net/manual/en/function.mt-srand.php http://master.php.net/manage/user-notes.php?action=edit+16502 http://master.php.net/manage/user-notes.php?action=delete+16502 http://master.php.net/manage/user-notes.php?action=reject+16502