atari2600land's Blog

Does the programming environment you're using to make Virtual Boy games really lack a RNG or PRNG? It sounds like an omission one would've made in the late 1970's. Anyway, I think you got some hints previously about various PRNGs and how to implement them. See also a programming thread in the Intellivision forum, I think it was First Spear. It turned a bit into theoretics about PRNGs as explained by intvnut. The principles for those should be possible to implement even in your environment if you don't have anything decent naively in terms of random calls.

You also perhaps need to come up with a good shuffling algorithm. A very good one is the Fisher-Yates Algorithm, also known as the Knuth Algorithm, or the Fisher-Yates-Knuth Algorithm.

 

https://www.i-programmer.info/programming/theory/2744-how-not-to-shuffle-the-kunth-fisher-yates-algorithm.html

 

It's as simple as:

 

 
for (int i = 0; i < data.Length; i++)
{
 swap(ref data[i], ref data[i+R.Next(data.Length-i)]);
}

 

Where "data[]" is your card array and "R.Next(n)" is the next random number generator from 0 to n.

 

-dZ.

I posted a fully working Galois implementation of PRNG on the Intellivision forums. It's in Assembly Language but it was based on this code:

 

 

 
#include <stdint.h>
uint32_t lfsr = 1;
unsigned period = 0;
 
do {
  /* taps: 32 31 29 1; feedback polynomial: x^32 + x^31 + x^29 + x + 1 */
  lfsr = (lfsr >> 1) ^ (-(lfsr & 1u) & 0xD0000001u);
  ++period;
} while(lfsr != 1u);

There are several things wrong with the code you provided. First off, I don't have a random number generator because there isn't one. Second, the assembler does not like swap. I am so confused by it right now. You'd need to look at the entire section I made about it to understand what I did and you seem so nice that I don't want to punish you by making you trudge through my code for it.

Chris, the LFSR you were looking for is within DZ-Jay's second reply above. You probably want to encapsulate it as a function call in order to use it muitiple times. My C is a bit rusty but I believe if you define local variables static (???) they will retain their value over multiple calls.