File squeezer

                         Jim Lopushinsky

                    Edmonton, Alberta, Canada

                        February 16, 1984


SQ has now been rewritten in assembly language.  As you will see,
it operates much faster than the old SQ program.   SQ is now 8080
compatable.

The program writer can utilize the squeezer by searching SQLIB in
the link step.  Only 2 external refrences are needed:

SQINIT:    This is the analysis phase.   SQ reads the input file,
and analyzes the file for squeezing.

     Input:    Register  HL contains the address of a scratch pad
               for  SQ.   This area of ram must be at least  3072
               (0C00h) bytes.

     Output:   Register A has the return code:

                    0    No errors
                    1    Input file is already squeezed
                    2    Input file is empty
                    3    Squeezed  file  will be larger then  the
                         input file.
                    4    Squeeze table or bit length overflow.

               Register HL contains the size (in sectors) of  the
               squeezed file.

               Register  DE contains the size (in sectors) of the
               input file.





SQ:    This is the squeeze subroutine.   It reads the input  file
again, and writes the squeezed file.

     Input:    Register  HL  contains the address of the FCB  for
               the  original  file  (so that  it  can  write  the
               filename in the squeezed file).

     Output:   Register A has the return code:

               0    No errors
               1    Abnormal  EOF  when reading the input file  a
                    second time.




SQINIT  itself has 5 external refrences,  3 of which are resolved
in SQLIB.  The 3 refrences in SQLIB are:

     MPBMUL    Multi-byte binary multiplication
     MPBDIV    Multi-byte binary division
     MPLSR     Multi-byte logical shift right


SQINIT requires 2 external refrences from the calling program for
byte  read and byte write.   These 2 subroutines are called  from
SQINIT  and  SQ to input unsqueezed  characters,  and  to  output
squeezed  bytes.   The 2 subroutines do not have to preserve  any
registers, and must return control with a RET instruction.

RDBYTE:    This the byte input subroutine.   One byte of data  is
passed back with each call to RDBYTE.

     Input:    none.

     Output:   Register A contains a byte of data for squeezing.

               Z flag clear (NZ true): byte of data passed.
               Z flag set (Z true): end of file reached.


WRBYTE:    This is the byte output subroutine.   One byte of data
is passed to WRBYTE with each call.

     Input:    Register A contains a squeezed byte of data.

     Output:   none.

     The WRBYTE subroutine must perform its own error recovery or
     termination.




The main program should do the following:

     1.   Open the input file
     2.   Call SQINIT
     3.   Check for error return from SQINIT
     4.   Re-open the input file
     5.   Open the output file
     6.   Call SQ
     7.   Check for error return from SQ
     8.   Close the output file



If there are any questions or comments, I can be reached at:

     (403) 484-5981    6:00 pm - 10:00 am @ 300/1200 baud