Re: gnubol: Re: ref touch points

[Michael McKernan <mck@tivoli.mv.com>]

>>>>> "Mike" == Michael McKernan <mck@tivoli.mv.com>
>>>>> wrote the following on Sat, 04 Dec 1999 12:22:23 -0500

  Mike> No, I have not made myself clear.  This is not a parsing
  Mike> issue.  Let's say we have the following records.

      01 A.			01 B.
         02 B.			   02 B.
	    03 C.		      03 C.
	       04 D.		         04 D.
	          05 X.			    05 Y.
		     06 Z PIC 9.	       06 Z PIC X.

  Mike> The programmer may legitimately reference Z of Y and it is a
  Mike> unique reference.  Since the name at the top of the tree need
  Mike> not be among the qualifiers, it becomes very inefficient to
  Mike> do the lookup top-down.  What we do instead, is form chains
  Mike> while we're building the symbol table of all the symbol table
  Mike> entries that have the same name, then use those chains to
  Mike> accomplish the lookup bottom-up.  We are now searching only
  Mike> the trees that contain the data-name instead of searching
  Mike> every tree in the program.

I should also have noted that when you start at an internal node and
search upward, you are searching only a single unique path to the top
of the tree.  In a top-down search, it is necessary to investigate
every branch.



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