This debugging session addresses Bug 111 in TDS version 99. The bug occurred when extracting product terms from an expression during the decompose command. Specifically, when extracting the third product term (PT3), the sub-chain that was extracted as the first product term (PT1) was removed. The solution was to check if the top node of an extracted product term has parents still in the container, and if so, update the parents to point to the extracted variable rather than the removed nodes. This prevents extracted sub-chains from being deleted during later extractions.

1. Debugging TDS
decompose bug 111
Fixed v99
By Daniel Gomez-Prado
09/16/2009
Disclaimer: This is not a tutorial.
This is a debugging session
for anyone working on TDS
http://www.dgomezpr.com/

2. Bug 111 at rev 88,…,99 on 09/09/16
b2
Trigger cmd: decompose
a2
Tds 01> poly (a+b)*(c+d+e*(a+b))
Tds 02> bottom b
Tds 03> bottom a
Tds 04> linearize
Tds 05> top a2
Tds 06> top b2
Tds 02> show -db
Tds 03> decompose e
e e
chains to extract:
e*b1, a2*e, b2*e*b1
PT1 PT2 PT3
problem!! b1 b1
Tds 04> show -db
// see next page for graph of the error
Fixed on ver 99

3. Steps b2
e Problem
b1
Solution must
come at this point
extractProductTerm before passing to
-> removeTermFromContainer another extraction
-> oneProductTerm

4. Problem
While extracting PT3:
------------------------------------------
extractProductTerm
-> removeTermFromContainer
-> oneProductTerm
------------------------------------------
The chain b2*e*b1 is deleted
because its top node b2 is not
marked, then the whole chain is
re-inserted again.
Problem: sub-chain e*b1 was
already extracted, and re-inserted
as PT1. But now e*b1 is gone.

5. Solution:
1. Right after finish extracting PT1
1. Check if its top node has parents
1. Normal case: (has no parents it’s a PO)
As we have just added this node to the container, and
we have not run the get parent, there should be no
parents for this node
2. Case Solution: (has parents in the container)
• Even though we removed these nodes, it turns out, that
the extracted form already existed in the container.
• Update the parents so they don’t point to the top of the
extraction, but to a single node with the same variable of
the extracted variable.
• Future chainOp (ie if we are in PT1, chains
corresponding to PT2 … PTn) need to be updated as
they still hold in their chains the nodes being replaced
by the extracted variable
• Solution taken.