uunalf was *not* written in C. no C compiler for the 6502 emits such
tight code, especially not the ones that were available in 1988. This
explains why it outperforms arc (which actually was in C) while having
a smaller executable size.

unalf14.com is a standard Atari segmented executable. For disassembly
purposes, I converted it to a single chunk of raw object code:

ataricom -n -m 1-2 unalf14.com unalf14.raw

IOCB usage:

#0 is E: as usual.
#1 is the input file(s).
#2 is K: (not sure if it's actually used).
#3 is the output file.

When the program exits (print_msg_complete), it checks the byte at
$0700 (BOOTRG). If it's equal to $53 (ASCII S, for SpartaDOS), it
exits via an RTS. Otherwise it exits via JMP (DOSVEC), which reloads
the DOS menu on DOS 2 and compatibles.

Bugs:

ALF14.COM won't actually compress any files at all, when run from
the DOS on the disk image I keep finding in archives. The DOS is
"XDOS". Whatever I try to compress, I always end up with a 0-byte
output file. It works better in DOS 2.0S, but "*.TXT" doesn't catch
all the files it should, either.

Trying to compress a file with the one-letter name D causes a an error
and the program exits. D:D works OK.

Compressed files:
-----------------------------------------------------------------------
original data:
ff ff ff ff 00 ff ff ff ff 01 ff ff ff ff 02
in binary:
00000000: 11111111 11111111 11111111 11111111 00000000 11111111  ......
00000006: 11111111 11111111 11111111 00000001 11111111 11111111  ......
0000000c: 11111111 11111111 00000010

compressed form:
10000000 00111111 11100000 01001111 11110000 00000100 00001101 11111110 00000001 10000011 00000000 10100000 00100000

-----------------------------------------------------------------------
orig in hex:
 aa aa aa aa 00 aa aa aa aa 01 aa aa aa aa 02

orig in bin:
 0: 10101010
 1: 10101010
 2: 10101010
 3: 10101010
 4: 00000000
 5: 10101010
 6: 10101010
 7: 10101010
 8: 10101010
 9: 00000001
10: 10101010
11: 10101010
12: 10101010
13: 10101010
14: 00000010

compressed:
 10000000 00101010 10100000 01001010 10100000 00000100 00001101 01010100 00000001 10000011 00000000 10100000 00100000 
in groups of 9 bits:
 1 00000000 0 10101010 1 00000010 0 10101010 0 00000000 1 00000011 0 10101010 0 00000001 1 00000110 0 00000010 1 00000001 0 0000

  0: 1 00000000 ; 0 start
  1: 0 10101010 ; literal $aa
  2: 1 00000010 ; 2: $aa $aa
  3: 0 10101010 ; literal $aa
  4: 0 00000000 ; literal $00
  5: 1 00000011 ; 3: $aa $aa $aa
  6: 0 10101010 ; literal $aa
  7: 0 00000001 ; literal $01
  8: 1 00000110 ; 6: $aa $aa $aa $aa
  9: 0 00000010 ; literal $02
 10: 1 00000001 ; 1 end

-----------------------------------------------------------------------
orig (sam.txt):
00000000: 49 20 61 6d 20 53 61 6d 0a 0a 53 61 6d 20 49 20  I am Sam..Sam I 
00000010: 61 6d 0a 0a 54 68 61 74 20 53 61 6d 2d 49 2d 61  am..That Sam-I-a
00000020: 6d 21 0a 54 68 61 74 20 53 61 6d 2d 49 2d 61 6d  m!.That Sam-I-am
00000030: 21 0a 49 20 64 6f 20 6e 6f 74 20 6c 69 6b 65 0a  !.I do not like.
00000040: 74 68 61 74 20 53 61 6d 2d 49 2d 61 6d 21 0a 0a  that Sam-I-am!..
00000050: 44 6f 20 79 6f 75 20 6c 69 6b 65 20 67 72 65 65  Do you like gree
00000060: 6e 20 65 67 67 73 20 61 6e 64 20 68 61 6d 3f 0a  n eggs and ham?.
00000070: 0a 49 20 64 6f 20 6e 6f 74 20 6c 69 6b 65 20 74  .I do not like t
00000080: 68 65 6d 2c 20 53 61 6d 2d 49 2d 61 6d 2e 0a 49  hem, Sam-I-am..I
00000090: 20 64 6f 20 6e 6f 74 20 6c 69 6b 65 20 67 72 65   do not like gre
000000a0: 65 6e 20 65 67 67 73 20 61 6e 64 20 68 61 6d 2e  en eggs and ham.
000000b0: 0a                                               .

Name          Length    Stowage    SF   Size now  Date       Time    CRC
============  ========  ========  ====  ========  =========  ======  ====
SAM.TXT            177       ALF   28%       128   8 Dec 82  12:24a  3690
  0: 1 00000000 ; 0 start
  1: 0 01001001 ; literal $49 I
  2: 0 00100000 ; literal $20
  3: 0 01100001 ; literal $61 a
  4: 0 01101101 ; literal $6d m
  5: 0 00100000 ; literal $20
  6: 0 01010011 ; literal $53 S
  7: 1 00000100 ; 4 (?)
  8: 0 00001010 ; literal $0a
  9: 0 00001010 ; literal $0a
 10: 1 00000111 ; 7 (?)
 11: 1 00000101 ; 5 (?)
 12: 1 00000010 ; 2 (?)
 13: 1 00001000 ; 8 (?)
 14: 0 00001010 ; literal $0a
 15: 0 01010100 ; literal $54 T
 16: 0 01101000 ; literal $68 h
 17: 0 01100001 ; literal $61 a
 18: 0 01110100 ; literal $74 t
 19: 1 00000110 ; 6 (?)
 20: 1 00000100 ; 4 (?)
 21: 0 00101101 ; literal $2d -
 22: 0 01001001 ; literal $49 I
 23: 0 00101101 ; literal $2d -
 24: 1 00000100 ; 4 (?)
 25: 0 00100001 ; literal $21 !
 26: 1 00001111 ; 15 (?)
 27: 1 00010001 ; 17 (?)
 28: 1 00010011 ; 19 (?)
 29: 1 00001011 ; 11 (?)
 30: 1 00010110 ; 22 (?)
 31: 1 00011000 ; 24 (?)
 32: 0 01101101 ; literal $6d m
 33: 1 00011010 ; 26 (?)
 34: 1 00000010 ; 2 (?)
 35: 0 01100100 ; literal $64 d
 36: 0 01101111 ; literal $6f o
 37: 0 00100000 ; literal $20
 38: 0 01101110 ; literal $6e n
 39: 0 01101111 ; literal $6f o
 40: 1 00010011 ; 19 (?)
 41: 0 01101100 ; literal $6c l
 42: 0 01101001 ; literal $69 i
 43: 0 01101011 ; literal $6b k
 44: 0 01100101 ; literal $65 e
 45: 0 00001010 ; literal $0a
 46: 0 01110100 ; literal $74 t
 47: 1 00011100 ; 28 (?)
 48: 1 00010100 ; 20 (?)
 49: 0 01101101 ; literal $6d m
 50: 1 00011111 ; 31 (?)
 51: 1 00011001 ; 25 (?)
 52: 1 00001001 ; 9 (?)
 53: 0 01000100 ; literal $44 D
 54: 1 00100101 ; 37 (?)
 55: 0 01111001 ; literal $79 y
 56: 0 01101111 ; literal $6f o
 57: 0 01110101 ; literal $75 u
 58: 0 00100000 ; literal $20
 59: 1 00101010 ; 42 (?)
 60: 1 00101100 ; 44 (?)
 61: 0 00100000 ; literal $20
 62: 0 01100111 ; literal $67 g
 63: 0 01110010 ; literal $72 r
 64: 0 01100101 ; literal $65 e
 65: 0 01100101 ; literal $65 e
 66: 0 01101110 ; literal $6e n
 67: 0 00100000 ; literal $20
 68: 0 01100101 ; literal $65 e
 69: 0 01100111 ; literal $67 g
 70: 0 01100111 ; literal $67 g
 71: 0 01110011 ; literal $73 s
 72: 1 00000011 ; 3 (?)
 73: 0 01101110 ; literal $6e n
 74: 0 01100100 ; literal $64 d
 75: 0 00100000 ; literal $20
 76: 1 00010001 ; 17 (?)
 77: 0 01101101 ; literal $6d m
 78: 0 00111111 ; literal $3f ?
 79: 1 00001001 ; 9 (?)
 80: 1 00100011 ; 35 (?)
 81: 1 00100101 ; 37 (?)
 82: 1 00100111 ; 39 (?)
 83: 1 00101001 ; 41 (?)
 84: 1 00101011 ; 43 (?)
 85: 0 01100101 ; literal $65 e
 86: 0 00100000 ; literal $20
 87: 1 00101111 ; 47 (?)
 88: 0 01100101 ; literal $65 e
 89: 0 01101101 ; literal $6d m
 90: 0 00101100 ; literal $2c ,
 91: 1 00110001 ; 49 (?)
 92: 1 00110011 ; 51 (?)
 93: 0 01101101 ; literal $6d m
 94: 0 00101110 ; literal $2e .
 95: 0 00001010 ; literal $0a
 96: 1 01010001 ; 81 (?)
 97: 1 00100110 ; 38 (?)
 98: 1 00101000 ; 40 (?)
 99: 1 00111011 ; 59 (?)
100: 1 01010101 ; 85 (?)
101: 1 00111110 ; 62 (?)
102: 1 01000000 ; 64 (?)
103: 1 01000010 ; 66 (?)
104: 1 01000100 ; 68 (?)
105: 1 01000110 ; 70 (?)
106: 1 01001000 ; 72 (?)
107: 0 01100001 ; literal $61 a
108: 1 01001010 ; 74 (?)
109: 1 01001100 ; 76 (?)
110: 1 00000100 ; 4 (?)
111: 1 01011111 ; 95 (?)
112: 1 00000001 ; 1 end
junk: 0000000
        ====  ========            ====  ========
Total      1       177             99%       128

-----------------------------------------------------------------------
orig: ABCDEFABBCCDDEEFABCABCDABCDEBCDBCDEBCDEF

  0: 1 00000000 ; 0 start
  1: 0 01000001 ; literal $41 A
  2: 0 01000010 ; literal $42 B
  3: 0 01000011 ; literal $43 C
  4: 0 01000100 ; literal $44 D
  5: 0 01000101 ; literal $45 E
  6: 0 01000110 ; literal $46 F
  7: 1 00000010 ; 2 AB
  8: 1 00000011 ; 3 BC
  9: 1 00000100 ; 4 CD
 10: 1 00000101 ; 5 DE
 11: 1 00000110 ; 6 EF
 12: 1 00000010 ; 2 AB
 13: 0 01000011 ; literal $43 C
 14: 1 00001101 ; 13 ABC
 15: 0 01000100 ; literal $44 D
 16: 1 00001111 ; 15 ABCD
 17: 0 01000101 ; literal $45 E
 18: 1 00000011 ; 3 BC
 19: 0 01000100 ; literal $44 D
 20: 1 00010011 ; 19 BCD?
 21: 1 00010010 ; 18 EB?
 22: 1 00000100 ; 4 CD
 23: 1 00000110 ; 6 EF
 24: 1 00000001 ; 1 end
junk: 0000000