SCSU, BOCU, and ISO 2022 (was: Re: Proposing UTF-21/24)

From: Doug Ewell (
Date: Fri Jan 26 2007 - 00:53:48 CST

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    Philippe Verdy <verdy underscore p at wanadoo dot fr> wrote:

    >> 1. Start with a "base" value.
    > Parse "base" here as the start of a codepage, reserve some values for
    > special codes likecontrols.
    >> 2. Encode each character as the difference between that character
    >> and
    >> the base.
    > which is completely equivalent to taking the code position in a
    > codepage

    OK, so you are saying the 128-character range that can be covered by a
    single byte in BOCU-1 is analogous to a 128-character C1/G1 code page.
    I don't quite agree, but I see your point.

    >> 4. Move the base after each use to minimize the length of jumps.
    > Which is for me exactly equivalent to using ISO2022 jumps...

    Not really. ISO 2022 has fixed, magic escape sequences to swap in
    different blocks. The mechanism for switching blocks is completely
    different from the mechanism for accessing characters within a block.
    BOCU-1 uses a calculated difference, just the same as it uses to encode
    any other character (except U+0000 through U+0020).

    >> 5. Space and C0 control characters get special handling.
    > Like are some codes in ISO2022...

    And SCSU. That's a minor similarity.

    > So for me, the IBM patent licencing on SCSU is protecting little, as
    > very small changes are needed to create something that would be in
    > fact nearer from past works, and could legitimately claimed as works
    > derived from prior works not under the IBM patent claims.

    I know for sure that was a mix-up.

    > And because the exact algorithm is patented but licenced for
    > royaltee-free use and distribution, what is the interest of keeping
    > such patent on it? Why IBM does not simply declare that the patent
    > will never be changed back to be payable for its use or
    > redistribution? Keeping the patent only as a security against
    > claimsmade by any concurrent that could acquire it and decide to
    > licence it differently against payments for its use and research?

    My opinion is that they are leaving the door open to change the
    licensing terms in the future.

    Doug Ewell  *  Fullerton, California, USA  *  RFC 4645  *  UTN #14

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