10位mt_rand（），带有无偏的第一个数字

Question

I want to generate the profile ids in my software. The mt_rand function works well but I need the ids to be a fixed 10 digit long. Currently I am looping through mt_rand outputs until I get a 10 digit number. But the problem I am facing now is that most of the profile ids start from 1 and some from 2. None from any of the other single digit numbers. I understand this happens because of mt_rand's range and it can't produce 10 digit numbers that start with 3 or more.

This is what I am currently doing

for($i = 0; $i < 200; $i++){
    $num = mt_rand();
    if(strlen($num) == 10) echo $num."<br>";
}

If you run the above code you will see all numbers start from either 1 or 2. Any way to fix this?

Edit: I guess I can just flip the numbers but some numbers end with zero and this seems like a bit of a hack anyways. But then again, random number generation is a hack in itself I guess.

Answer 1

just start your IDs at 1000000001 , then ID 2 at 1000000002 , ID 543 at 1000000543 , and so on?

alternatively, keep calling mt_rand(1000000001,min((PHP_INT_SIZE>4 ? intval("9999999999",10): PHP_INT_MAX),mt_getrandmax())) until you get an ID which does not already exist in your database? (this will be more and more cpu intesive as your db grows larger and larger.. when its almost full, i wouldn't be surprised if it took billions of iterations and several minutes..)