Re: [0.99-15] Some problems and questions

["John E. Davis" <davis>]

Paul <p.boekholt@xxxxxxxxx> wrote:
>In linux.sl, this is set to -1 but linux.sl is not loaded by default so it's
>0. On my previous PC, a 486-66, I noticed scrolling in the console takes a
>lot of CPU time if I leave it to 0. Setting it to -1 doesn't seem to stop
>the recentering, but setting it to 1 will cause it to jump much more. What do
>-1 and 1 mean?

It dates from a time when the terminfo files were not very accurate.
Hence a mechanism was added to allow an easy way to indicate that the
terminal has this capability.  In particular, the linux console had
the capability to scroll, but was poorly implemented.  So, I added a
hack such that -1 means, yes the terminal can scroll but not very
well.

To give you an idea about what I mean by "not very well", consider an
analogy to how the linux console scrolling was (and still may be)
implemented.  Suppose that is is desired to move

    ABCDEFGHIJLKMNOPQRSTUVWXYZ

to

          ABCDEFGHIJLKMNOPQRSTUVWXYZ

One way is through the sequence of operations:

    ABCDEFGHIJLKMNOPQRSTUVWXY      Z
    ABCDEFGHIJLKMNOPQRSTUVWX      YZ
    ABCDEFGHIJLKMNOPQRSTUVW      XYZ
        .
	.
    A      BCDEFGHIJLKMNOPQRSTUVWXYZ
          ABCDEFGHIJLKMNOPQRSTUVWXYZ

The algorithm in the linux kernel used a recursive algorithm:

    ABCDEFGHIJLKMNOPQRSTUVWXYZ
    ABCDEFGHIJLKMNOPQRSTUVWXY Z
    ABCDEFGHIJLKMNOPQRSTUVWX YZ
    ABCDEFGHIJLKMNOPQRSTUVW XYZ
        .
	.
    A BCDEFGHIJLKMNOPQRSTUVWXYZ
     ABCDEFGHIJLKMNOPQRSTUVWXYZ
     ABCDEFGHIJLKMNOPQRSTUVWXY Z
     ABCDEFGHIJLKMNOPQRSTUVWX YZ
        .
	.
	.
         ABCDEFGHIJLKMNOPQRSTUVWXY Z
         ABCDEFGHIJLKMNOPQRSTUVWX YZ
	    .
	    .
	    .
         A BCDEFGHIJLKMNOPQRSTUVWXYZ
          ABCDEFGHIJLKMNOPQRSTUVWXYZ
	
--John
     

    



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