How random is rand()?

Hi Rob,

Here is a method we used for a customer to generate a unique ID per HTTP request:

 
 when RULE_INIT { 
  
     Initialize 10 variables to track the distribution of first digits 
    for {set i 0} {$i < 10} {incr i} { 
       set $i 0 
    } 
  
     Loop through and generate X number of random numbers 
    for {set i 0} {$i < 1000} {incr i} { 
  
        Save a new random number 
       set random_number [expr {rand()}] 
       set random_number_float [format %0.10f $random_number] 
  
        Log the random number, the formatted string and the first digit 
       log local0. "$random_number, [format %010s [string range $random_number 2 12]],\ 
          [string range [format %010s [string range $random_number 2 12]] 0 0], $random_number_float" 
  
       incr [string range [format %010.f [string range $random_number_float 2 12]] end end] 
    } 
    log local0. "Summary: " 
    for {set i 0} {$i < 10} {incr i} { 
       log local0. "$i: [set $i]" 
    } 
 } 
 

For a run of 100,000 iterations, the distribution is fairly even:

Rule : Summary:

Rule : 0: 10114

Rule : 1: 9981

Rule : 2: 9781

Rule : 3: 9980

Rule : 4: 10104

Rule : 5: 9993

Rule : 6: 10074

Rule : 7: 10067

Rule : 8: 10013

Rule : 9: 9893

I got the basics from this TCL wiki page (http://wiki.tcl.tk/17696). I didn't seed rand as there were a few people stating:

as specifying our own seed for every call to roll is more likely to reduce randomness than improve it, I've left it out altogether.

Aaron