Comparing ColdFusion Number Randomization Algorithms

The other week, I posted about how I didn't feel like ColdFusion always did a great job of random number generation. When using ColdFusion's RandRange() method, I just pass in the two required integers. After posting this, Dustin told me that ColdFusion MX7 introduced a third argument for the RandRange() method, which was the algorithm by which the random numbers were generated. By default, ColdFusion uses the CFMX_COMPAT algorithm. Apparently (and this is stated directly in the documentation), the alternate algorithm, SHA1PRNG, will do a much better job of randomizing numbers.

To explore these two algorithms, I first wanted to start out graphing them, to see if I could see any obvious trends. In the following example, I am looping over the two algorithms and then using ColdFusion's CFChart tag to charge 50 random numbers between the values 1 and 50.

From the above code, we get the following graphs:

Algorithm: CFMX_COMPAT (ColdFusion's Default)

Algorithm: SHA1PRNG (Added in ColdFusion MX7)

Now, I look at these two graphs, and frankly, they don't mean anything to me. I don't see trends, and even if I do see some trends, I don't understand the significance. Both of these graphics look like a nice randomized set of numbers.

But more than that, this is not a useful test case for me. My issues with randomness rarely involve generating a ton of numbers right in a row; my scenarios usually involve manually refreshing a page to see if something is rotating "properly" (think advertisements or header images). In that case, there is a big delay between random number generation (compared the delay between CFLoop iterations). In my next experiment, I am using a META tag refresh to put a uniform delay between my page refreshes as this will most closely mimic me sitting there and hitting the browser's refresh button:

I ran the above code three times for each algorithm and here are the number lists that were generated:

Algorithm: CFMX_COMPAT (ColdFusion's Default)

• 9,7,7,7,7,7,7,6,6,6,6,9,9,8,9,8,8,8,8,8
• 3,6,6,6,5,6,6,5,5,4,4,5,2,3,2,2,2,2,2,2
• 5,8,8,7,7,6,7,7,6,6,9,10,9,9,8,8,9,8,8,8

Algorithm: SHA1PRNG (Added in ColdFusion MX7)

• 6,8,9,6,4,5,5,9,8,4,10,5,7,4,4,8,10,2,6,1
• 6,6,8,9,8,1,8,9,9,3,7,3,3,5,6,7,7,3,4,5
• 4,8,2,8,4,1,4,4,3,3,9,10,2,10,6,6,4,4,5,2

Just looking at these numbers, I can clearly see grouping in the CFMX_COMPAT algorithm. There is some grouping in the SHA1PRNG algorithm, but to a much much lesser degree. I don't know how the timing of the random number generation affects things, but it seems to have some sort of a link to the seemingly effective nature of the outcome. Now, I say "seemingly" because, remember, I am really more concerned about an even distribution of numbers and less so about the actual randomization of the numbers. Randomization or not, the SHA1PRNG seems to have a better distribution of numbers.

What Other People Are Searching For

[ local search ] coldfusion random number generation
[ local search ] random numbers in coldfusion
[ local search ] better randomization in coldfusion
[ local search ] getting random number in coldfusion
[ local search ] creating random number in coldfusion
[ local search ] cfmx_compat vs sh1prng
[ local search ] sh1prng better algorithm coldfusion

You Might Also Be Interested In: