2020-05-24

I’ve managed to solve a number picking algorithm that I’m happy with the performance of in NextBASIC. It’s a Fisher Yates sort, then picking the first 4 items (actually I cut the sort at the fourth iteration).

#autoline 10,10
%N=20: ; select from 0-20 (excluding 20)
%P=4: ; pick 4 numbers
; init the 0-N array
REPEAT
  %S(i)=%i
  %i=%i+1
REPEAT UNTIL %i=N
REPEAT
  %T=% RND i
  %W(N-i)=%S(T)
  %i=%i-1
  %S(T)=%S(i)
REPEAT UNTIL %i=(N-P)
; the picked results are stored in W

Now I need to check this array when the tomb is surrounded. I could check the whole of this array each time the tomb is surrounded, but it makes more sense to add which are the “winning” tombs to the tomb array(20) I already have.

The tomb array itself holds it’s state in bit values. As such, the current line of code for marking one side of a tomb as “completed” looks like this (horribly):

IF %k THEN %T[g]=%T[g]&@11111101:%T[h]=%T[h]&@11110111: ; new line for readability
ELSE %T[g]=%T[g]&@11111011:%T[h]=%T[h]&@11111110

The low nibble represent the side of the tomb that has been completed, and the high nibble for whether the tomb has been unlocked already:

0x01=top
0x02=right
0x04=bottom
0x08=left
0xF0=tomb has been unlocked

So the IF statement from earlier is always run and always applies the logical & but this is to create consistent timings. Normally, in modern coding, I’d avoid unnecessary code execution, but with NextBASIC to get the game to run at a consistent speed, I’m making sure that each loop does roughly the same amount of work.

Thus far I’m only using 8 bits of the value to indicate the status of the tomb and I need to be able to flag the tomb to say what’s contained inside of it, either a scroll, a mummy, a key, a tomb or nothing at all. I could keep all this data inside a single byte, but the integers in NextBASIC as 16bit so I could also expand out to the high byte to store the value of the tomb.

Meh. I prefer to be efficient, so how about this:

0x00-0x04=tomb contents
0x08=tomb has been unlocked
0x10=top
0x20=right
0x40=bottom
0x80=left

This shifts around where the data is stored, but I put the wall status on the high nibble for simplicity, so that I can then do something like %T = %T + INT (key) and set key = 3 somewhere as a constant (though in reality I’ll stick to integer expressions).

Originally published on Remy Sharp’s b:log