rnginfo.pl

#!/usr/bin/perl

# randinfo.pl
#  by Drusepth 10/05/2007

# Purpose:
# When using random numbers in programs, sometimes you want them to be
# actually random.  But other times, (for example, if you were coding a 
# lottery machine) you would want to know the probability a user would 
# hit a jackpot (three consecutive 7s).  This program calculates the 
# percentage of NUMBER passed returning as a result of rand() with the
# passed SEED.  With the information recieved, a programmer could decide
# on a seed that would be more fit for what they were writing.

$seed = shift or die 
'----------------------------------------------------------------------
 Usage: perl randinfo.pl SEED [NUMBER]
   Where SEED is the seed used to seed the rand() function.
   and NUMBER is the number to look for the percentage of being a 
   result.
 If NUMBER is omitted, the script will write the possibilities of the
 numbers 0 through a set number ($max_omitted) to a text file 
 specified in the code as $output_file.
 If $output_file exists at the time of running, it will be overwritten.
----------------------------------------------------------------------' 
. "\n";

$number = shift or $write = 1;

# Seed the random numbers:
srand($seed);

#                              Tweaks:                               #
# When generating random numbers, this will be the max result possible.
$max_number = 100; 
# This is the output file to use if writing to a file.
$output_file = "randinfo-" . $seed . ".txt";
# When a number to look for is omitted, look at all numbers between 
# this number and 0.  If this is above $max_number, it will be 
# set to equal $max_number upon runtime.
$max_omitted = 100;
# When gathering the probability of recieving a number, this is the
# number of random numbers to generate, multiplied by $max_number.
# The higher the number, the more accurate the results, but it may
# also take a longer time for the script to run.
# Reasonable settings are 10 to 10000.
$repeat = 1000;
# This is the number of decimal places to go to when printing the results.
# Leave blank for no rounding.
$decimal_fix = 6;

if ($write == 1) {
   print "Working...\n";
   # Find probabilities of numbers 1 through $max_omitted and write
   # to $output_file.

   $max_omitted++;
   $max_number++;

   # Make sure the number of numbers to check isn't more than the
   # max number that a random number can be.
   if ($max_omitted > $max_number) {
      $max_omitted = $max_number;
   }

   # First, initialize the results array.
   for ($i = 0; $i < $max_omitted; $i++) {
      $results[$i] = 0;
   }

   # Then, generate random numbers inside the for loops and increment
   # the corresponding value in @results.
   for ($j = 0; $j < ($repeat * $max_number); $j++) {
      $random = int(rand($max_number));
      $results[$random]++;
   }

   # The results array is full.  Output to the terminal
   $i = 0;
   # Print the header:
   print "Number\t-\tResults\t-\tPercent\n";
   # Put everything to be printed in $string.
   foreach $result (@results) {
      $percent = ($result / (($max_number * $repeat) + 0.5) * 100);
      $percent = substr($percent, 0, $decimal_fix + 2);
      $string .= "$i\t-\t$result\t-\t$percent%\n";
      $i++;
   }
   # Find the most- and least- used numbers and add them to $string.
   # The least values are set high intentionally.
   $max_i = 0;
   $max_number = 0;
   $least_i = 100000000000;
   $least_number = 1000000000000;
   foreach $result (@results) {
      if ($result > $max_number) {
         $max_i = $i;
         $max_number = $result;
      }
      if ($result < $least_number) {
         $least_i = $i;
         $least_number = $result;
      }
      $i++;
   }
   $string .= "\n-------------------------------------------------\n";
   $string .= "Result Statistics:\n";
   $string .= "Most Used: $max_i at $max_number occurences.\n";
   $string .= "Least Used: $least_i at $least_number occurences.\n";
   $string .= "-------------------------------------------------\n\n";
   # Print to the file
   print $string;
   $error = "*** Error: Couldn't open/create $output_file for writing!\n";
   if (open(RESULTS, $output_file)) {
      $i = 0;
      foreach $result (@results) {
         $percent = ($result/(($max_number*$repeat)+.5)*100);
         $percent = substr($percent, 0, $decimal_fix + 2);   
         print "$string";
         $i++;
      }
      close(RESULTS);
   } else {
      print $error;
   }
} else {
   print "Working...\n";
   # Find how often a number occurs in the given seed.
   
   # Do ittt
   $occurences = 0;
   for ($i = 0; $i < 1000000; $i++) {
      if (int(rand($number * 100)) == $number) {
         $occurences++;
      }
   }
   $num_inc = $number * 100;

   # Print to the terminal 
   $string = "When generating one million random numbers with the seed $seed
and a max result of $num_inc, $number occurs $occurences times.  ";
   $string .= "(" . ($occurences / 1000000) * 100 . "%)\n";
   print $string;
}