Dr. Jay
Account closed
Registered: Jan 2003
Posts: 32 |
Random Numbers
Just wanted to share. This has probably been discussed a million times, but in case it hasn't ... was doing a search for random numbers. Some of the old hardware tricks like $d800 don't work with specific versions of the machine and certainly not in all emulators. I found this snippet of code which, if I remember correctly, was from boulderdash:
random eor $dc04
eor $dc05
eor $dd04
adc $dd05
eor $dd06
eor $dd07
rts
Tried using it - I always test random numbers by using the sequence to plot pixels. If you have a bad generator, you can easily see patterns. I could tell this pattern above was clustering on byte-boundaries after watching a few minutes in the plotter. I felt like it was because it was synched too much to the timers and that something would have to throw it out. Then I started thinking about how stable rasters are a $#$@#$@$ and if the call to this routine doesn't always come on a stable raster then we'll have some cycles out of synch ... so I made this simple modification:
random lda #$00
eor $dc04
eor $dc05
eor $dd04
adc $dd05
eor $dd06
eor $dd07
sta random+1
rts
And it appears to work like a charm - much more random! Just uses a seed to feed into the timer sequence, rather than the timer sequence alone!
|
