Assembly-time LZW compression

Here comes one of the things I was very eager to try with the new fasm 1.71 features. It's a proof-of-concept code that shows the ability of new fasm to compress some code or data at assembly time. With earlier LOAD/STORE abilities the code could only be rewritten in place, which allowed encoding it but not compression.

To make an example I implemented the LZW algorithm, which is a very simple one and thus it was relatively easy task. This is straightforward implementation and it will be slow on any larger data - nonetheless it shows that the abilities of fasm have improved again.

Code:

virtual at 0
  __data::

      db "Some data to compress...",13,10

      file "test.txt"

  .size = $
end virtual



__LZW__MAX_ENTRIES = 4096

virtual at 0
  __LZW__table::
  dd __LZW__MAX_ENTRIES dup (?,?)
end virtual

__LZW__count = 102h

__LZW__last_byte = 0
__LZW__bit_offset = 0

macro __LZW__write data {
  local c,d,p
  d = __LZW__count-1
  c = 0
  while d
    d = d shr 1
    c = c + 1
  end while
  d = data
  while c > 0
    if __LZW__bit_offset + c >= 8
      p = 8 - __LZW__bit_offset
      db __LZW__last_byte or (d and (1 shl p - 1)) shl __LZW__bit_offset
      __LZW__last_byte = 0
      __LZW__bit_offset = 0
      c = c - p
      d = d shr p
    else
      __LZW__last_byte = __LZW__last_byte or d shl __LZW__bit_offset
      __LZW__bit_offset = __LZW__bit_offset + c
      c = 0
    end if
  end while
}

dictionary_code = 0
string_offset = 0
string_length = 0
scan_from = 102h

while string_offset + string_length < __data.size

  string_length = string_length + 1

  if string_length = 1

    load dictionary_code byte from __data:string_offset

  else

    in_dictionary = 0

    repeat __LZW__count - scan_from
       load entry_offset dword from __LZW__table:(scan_from+%-1)*8
       load entry_length dword from __LZW__table:(scan_from+%-1)*8+4
       if string_length = entry_length
         equal = 1
         repeat string_length
           load a byte from __data:string_offset+%-1
           load b byte from __data:entry_offset+%-1
           if a <> b
             equal = 0
             break
           end if
         end repeat
         if equal
           in_dictionary = 1
           dictionary_code = scan_from+%-1
           scan_from = scan_from+%
           break
         end if
       end if
    end repeat

    if ~ in_dictionary

      __LZW__write dictionary_code

      store dword string_offset at __LZW__table:__LZW__count*8
      store dword string_length at __LZW__table:__LZW__count*8+4
      __LZW__count = __LZW__count+1

      if __LZW__count>=__LZW__MAX_ENTRIES-1
        __LZW__write 100h
        __LZW__count = 102h
      end if

      string_offset = string_offset+string_length-1
      string_length = 0
      scan_from = 102h
    end if

  end if

end while

if string_length > 0
  __LZW__write dictionary_code
  __LZW__count = __LZW__count+1
  __LZW__write 101h
end if

if __LZW__bit_offset > 0
  db __LZW__last_byte
end if