Naive Noel Nibbles

Author: sixxie
Category: Christmas Challenge
System: Dragon 32
Language: Dragon BASIC (Microsoft Extended)
Len source code: 181
Len exe file:    928
Len code only:   157
Instructions:
 Use XRoar and ensure you have the BASIC ROM (d32.rom).  From the
 command line:
     xroar -m dragon32 -load nnn.cas
 .
 Or use MAME, with similar ROM requirements.  From the command line:
     mame dragon32 -ext '' -cass nnn.cas
 .
 Either way within the emulated machine, load and run with:
     CLOAD
     RUN
Description:
 Simple encoding of the left half of each line into pairs of ASCII
 characters representing five bits each.  The reflection for the right
 half of each line is built up as the left is printed a character at
 a time.
 .
 I tried to get something out of vertical symmetry, but my BASIC-fu is
 not strong enough and it ended up a few bytes longer, even though the
 "input" string was half the length.
 .
 Because the Dragon's text screen is only 16 rows high, the top of the
 pattern will scroll off the screen as the rest is printed.
Comments:
 Loading one of many programs that redirect BASIC to hi-res graphics can
 allow you to see the whole output on screen at the same time, but this
 is optional and not part of the submission.
 .
 Sizes: source is the ASCII text version, exe is the tokenised BASIC
 with cassette leaders, blocking, etc., code only is the difference
 between PRINT MEM before and after loading the program.
 .
 Noel Nibbles are clearly a little more generous than those at other
 times of the year.