php rand function

[nmts]

Can anyone explain how this function actually works? Is there a way to write your own random function? Not that I need to, but it would be cool to understand it

[krillz]

Can anyone explain how this function actually works? Is there a way to write your own random function? Not that I need to, but it would be cool to understand it

 

php's rand() function is based on so called pseudo-random numbers.

A pseudo-random number is based on on a formula that would look random to anyone that does not know the formula. And based on a quote from a book covering the topic of random functions, this formula should have the following characteristics:

 

Good numeric distribution, let say you want to produce a random number between 0 and 5 then the formula should produce a equal ammounts of 0 - 1 - 2 - 3 - 4 - 5 over time.

 

You should not be able to predict the numbers, unless you know the formula and the start value used in the formula.

 

The process should not cycle, in other words produce the same set numbers over x number of intervalls.

 

So it's not really random, but it seems random to the user.

 

If you check major online casinos they generate random numbers using nature, most common is using materials that randomly discharges photons to trigger a number, or use radioactive isotops as radio active decay is random by nature you can never predict when a "burst" happens, using this you will achieve "true" randomness by measuring when this happens.

 

*edit*

check php's better random function called: mt_rand() as it's much faster than rand() and uses the Mersenne Twister method to generating numbers.

Edited February 27, 2010 by krillz