RE: Least used parts of BMP.

From: John Dlugosz (
Date: Fri Jun 04 2010 - 12:03:06 CDT

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    > -----Original Message-----
    > From: [] On
    > Behalf Of Doug Ewell
    > That said, if Kannan were to go with the alternative format suggested
    > on
    > this list:
    > 0xxxxxxx
    > 1xxxxxxx 0yyyyyyy
    > 1xxxxxxx 1yyyyyyy 0zzzzzzz
    > then he would at least have this one feature of UTF-8, at no additional
    > cost in bits compared to the format he is using today.

    Yes, the cost in bits is the same. Fast gulping of stream input is one difference, but having the encoded form contain, literally, the unencoded form makes it particularly simple. Just read the bytes into a variable and mask off the high bits. With the distributed bit, it has to be masked and shifted and OR'ed in 7 bits at a time. For the general form using very large words (e.g. cryptographic keys), the encoded form is just a prefix followed by the _same_ bytes that you want stored in the memory block, whose length you know.

    > Of course, he will not have other UTF-8-like features, such as
    > avoidance
    > of ASCII values in the final trail byte, and "fast forward parsing" by
    > looking at the first byte. He may not care. One thing I've noted
    > about
    > descriptions of UTF-8, in the context of alternative formats for
    > private
    > protocols, is that they always assume these features are important to
    > everyone, when they may not be.

    For sure. A compressed stream will not be random-access and will include other mechanisms such as checksums. A storage format can be very different from the manipulation format.

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