dos33fsprogs/basic/z

Executable ASCII decoding.
Here's the encoder source.
It requires a 65C02, though, to save one byte.  I would like to fix
that somehow.

How it works:

On entry:
- X=$9D;
- Y is the low byte of the CALL target;
- carry is clear;
- $7D-7E is $800;
- $B8-B9 points to the token after the CALL;
- $73-74 points to $9600;
- $6F-70 points to $9600.

        dex                     ca              *
        dex                     ca              *
        dex                     ca              *
        dex                     ca              *
        dex                     ca              *
        dex                     ca              *

Sets X to $97, so we can use it later.

        dey                     88              GR

Skip the opening quote (it's read backwards) in the 6-bit table.

--      inc     $b8             e6      b8      ASC     DEF

Skip the opening quote in the 2-bit table.

        lda     ($21,x)         a1      21      POP     !

Read from 2-bit table (at $B8).

        adc     #$5c            69      5c      i       \

Move into $80+ range, guarantees a bit is set so we don't exit early.

        sta     $30             85      30      DEL     0

Save for later.

-       dey                     88              GR
        lda     ($7d),y         b1      7d      RETURN  }

Read from 6-bit table.

        adc     #$5c            69      5d      i       \

Move into $80+ range, always sets V flag because bit 6 and bit 7 are
inverted in our data (V will be cleared when we read a value < $24,
specifically the closing quote).
        lsr     $30             46      30      F       0
        ror                     6a              j
        ror                     6a              j
        ror                     6a              j
        ror                     6a              j
        ror                     6a              j
        ror                     6a              j
        ror                     6a              j
        lsr     $30             46      30      F       0
        ror                     6a              j

2-bit table carries bits 7 and 0.

        sta     ($dc,x)         81      dc      FOR     LOG

Write through ($73).

        inc     $73             e6      73      ASC     s

Move next.

        lda     $30             a5      30      ONERR   0
        dec                     3a              :
        dec                     3a              :
        bne     -               d0      e5      =       VAL

Loop while a bit is set.

        bvs     --              70      db      p       RND

Loop while our data are read.

        jmp     ($6f)           6c      6f      l       o

Jump $9600.