Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!samsung!olivea!uunet!aurs01!whitcomb From: whitcomb@aurs01.UUCP (Jonathan Whitcomb) Newsgroups: comp.dcom.fax Subject: Re: 2-d encoding and padding EOL Message-ID: <59686@aurs01.UUCP> Date: 28 Mar 91 17:22:00 GMT References: <41468@ucbvax.BERKELEY.EDU> Sender: news@aurs01.UUCP Reply-To: whitcomb@aurw97.UUCP (Jonathan Whitcomb) Organization: Alcatel Network Systems, Raleigh NC Lines: 54 In article <41468@ucbvax.BERKELEY.EDU> sam@oxford.berkeley.edu (Sam Leffler) writes: -If you're padding the EOL indicator to a byte boundary (say -for a modem or when placing data in a file), does the tag bit -used to signal the type of the next row in 2-d encoded data -go *in the byte*, or after? That is, should the EOL byte include -the tag bit, or does the tag bit go in the immediately following -byte? What do you mean EOL byte? The EOL character is 13 bits long. -Putting the bit in with the EOL is a lot more convenient, -but it seems like the tag bit is logically part of the line of data -and so belongs after. Considering that the protocol is bit oriented, and not byte oriented, why do you care? Just keep packing the bits into bytes until you get an EOF (which is six consecutive EOL's, if memory serves). Any software that is reading the file should not be sensitive to byte boundaries either. If for some reason you want to have each line of data to line up on byte boundaries, just pad the EOL with leading zeros (which will be ignored). The tag bit is defined as the bit after the EOL character for 2-d coding. The tag bit indicates whether the *following* line will be one or two dimensionally encoded, so I would assume you want to keep it with the EOL character. Considering that 2-d encoded lines always depend on the preceding line for reference, it should be pretty arbitrary where you put the bit, but my inclination would be to keep it with the EOL character. -TIFF Class F has an option that says to pad EOL's to byte -boundaries, but does not specify which of the two cases is to -be used. Modem manufacturers that have controls for padding -EOLs to byte boundaries don't seem to acknowledge 2-d encoded -data. I've looked in the CCITT specs, and they seem to indicate -that the tag bit goes with the row it "modifies". Where in CCITT Rec T.4 do you see this? - - Sam - -sam@sgi.com Perhaps I just don't understand your application. Jonathan ********************************************************************** Jonathan Whitcomb UUCP: Alcatel Network Systems, Raleigh, NC Delphi: JBWHIT