New subject: Character/column confusion in Mule [was: Are long line caches useful?]

Thursday, 3 September 1998


        Do you think this particular FSF Emacs feature is truly useful?  I
wanted to devote some time implementing it, but then I concluded that
it is in 99.99% cases utterly useless, and that I have better things
to do with my time.

    *** Faster processing of buffers with long lines

    The new variable cache-long-line-scans determines whether Emacs
    should use caches to handle long lines more quickly.  This variable is
    buffer-local, in all buffers.

    Normally, the line-motion functions work by scanning the buffer for
    newlines.  Columnar operations (like `move-to-column' and
    `compute-motion') also work by scanning the buffer, summing character
    widths as they go.  This works well for ordinary text, but if the
    buffer's lines are very long (say, more than 500 characters), these
    motion functions will take longer to execute.  Emacs may also take
    longer to update the display.

    If cache-long-line-scans is non-nil, these motion functions cache
    the results of their scans, and consult the cache to avoid rescanning
    regions of the buffer until the text is modified.  The caches are most
    beneficial when they prevent the most searching---that is, when the
    buffer contains long lines and large regions of characters with the
    same, fixed screen width.

    When cache-long-line-scans is non-nil, processing short lines will
    become slightly slower (because of the overhead of consulting the
    cache), and the caches will use memory roughly proportional to the
    number of newlines and characters whose screen width varies.

    The caches require no explicit maintenance; their accuracy is
    maintained internally by the Emacs primitives.  Enabling or disabling
    the cache should not affect the behavior of any of the motion functions;
    it should only affect their performance.

-- 
Hrvoje Niksic <hniksic(a)srce.hr&gt; | Student at FER Zagreb, Croatia
--------------------------------+--------------------------------
`VI' - An editor used by those heretics that don't subscribe to
       the Emacs religion.

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Are long line caches useful?