LZW compression and binaryEncode

[jbv]

Frank,

Thanks for the reply, and for the code.
Actually, I know how to represent numbers in binary
or hexadecimal (I did quite a bit of assembler prog.
several years ago).
What I was wondering was rather : if I need 9 bits to
represent my numbers, shall use 2 characters (using the
least significant bit of the 2nd char for the 9th bit, and
leaving the 7 other bits to 0), or is there a more compact
way of representing it (without leaving any extra bit to
0) ?
Again, the binary output needs to be compatible with the
pdf filter for standard LZW compression...

Thanks,
JB

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> A character cannot store values outside the range of 0-255.  if you
> wish to store longer values, you need to use multiple characters.  For
> example, you can use two characters to store values in the range of
> 0-65535:
>
> function encode2 x
>    return numToChar(x div 256) & numToChar(x bitAnd 255)
> end encode2
>
> function decode2 x
>    return (charToNum(char 1 of x) * 256) + charToNum(char 2 of x)
> end decode2
>
> On Apr 17, 2005, at 5:07 PM, jbv wrote:
>
> >
> >
> > Dar,
> >
> > Thanks again for the reply, but actually I know most of
> > what you explained, as I've already fiddled with the
> > binaryEncode function (for sound files & other data
> > manipulations)...
> > Although, several issues still remain unclear : my serie
> > of output indexes resulting from the LZW compression
> > feature more than 256 entries. Therefore I'm wondering
> > how this could be represented in binary, in order to be
> > decoded by the LZW filter in pdf...
> >
> > Best,
> > JB
> >
> >> On Apr 17, 2005, at 2:38 PM, jbv wrote:
> >>> But now I need to convert the output serie of index into binary
> >>> data... Anyone familiar with this ?
> >>> I guess I need to use binaryEncode, but how to set up parameters ?
> >>
> >> Normally, we think of a value in Transcript as a sequence of
> >> characters.  When we work with binary we can view each character as
> >> that for an 8-bit encoding, that is, a byte.  Thus, a value can be
> >> viewed as a sequence of bytes.  Just as we can concatenate characters
> >> with &, we an concatenate what we consider to be bytes sequences the
> >> same way.
> >>
> >> To get at the numerical value of the byte, you can use charToNum().
> >> You can also use numToChar() as the inverse.
> >>
> >> You can also use binaryEncode() and binaryDecode().  Most formats are
> >> in host order and so are of limited utility.  However, some formats,
> >> such as "N", are big endian.  If you need small endian formatting,
> >> just
> >> reverse.  There are some formats missing, so you would want to build
> >> up
> >> a few simple functions to help.
> >>
> >> For example,
> >>
> >>     put binaryEncode("N",566) into aLen
> >>
> >> would put 4 bytes (chars) into aLen.
> >>
> >> Dar
> >>
> >> --
> >> **************************************************
> >>      DSC (Dar Scott Consulting & Dar's Lab)
> >>      http://www.swcp.com/dsc/
> >>      Custom libraries (with externals, if needed)
> >> **************************************************
> >>
> >> _______________________________________________
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> >
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> - -----------------------------------------------------------
> Frank D. Engel, Jr.  <fde101 at fjrhome.net>
>
> $ ln -s /usr/share/kjvbible /usr/manual
> $ true | cat /usr/manual | grep "John 3:16"
> John 3:16 For God so loved the world, that he gave his only begotten
> Son, that whosoever believeth in him should not perish, but have
> everlasting life.
> $
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