snowflake (6502) 1.0

Author: David Payne
Category: Christmas Challenge 2025
System: BBC Micro
Language: 6502 assembly language
Len source code: 529 bytes
Len exe file: 64 bytes
Len code only: 64 bytes
Instructions:
Save the VCCC25.ssd file on your local PC
From the https://bbc.xania.org website
click on Discs
From examples or local
Choose file
select the saved VCCC25.ssd file
enter *RUN 6502

Description:
The snowflake is mostly encoded as bits in 9 bytes of data. This is possible due to the symmetry.

the algorithm is along the lines of:
data = [73,146,4,9,114,48,81,2,0]
dir = -1
x = 9
repeat
   for y = -9 to 9
      if x = 0 or y = 0 then
         print "*";
      else
         i = abs(y)
         a = data[x-1]
         repeat
            LSR a
            i = i - 1
         until i = 0
         if carry flag is set then
            print "*";
         else
            print " ";
         end if
      end if
   next y
   print
   x = x + dir
   if x = 0 then dir = 1
until x = 10

Comments:
It was a bit trickier this year, but still fun. Thanks to Logiker for running this contest again.