Re: help with a logic algorithm

Thiago Adams:

the algorithm is be used in flow analysis of C code.  I
realized my previous approach will not work because I also
need intermediate result.
>
for instance
>
if (p && p->i) {}
>
I need to know p is not-null after && , I cannot wait
until the end of expression. The algorithm must propagate
the results.  I am thinking on alternatives..

Then your original idea of analysing the expression tree is
good: the algorithm will be linear for conjunction and
negation, but will branch over disjunction. The short-
circuit evaluation may be accounted for by, eg., stroring
the known invariants with each node. For (a || b) you will
have:

OR
   a
   b [a is false]

yielding two branches: 1) a and 2) !a && b .

I do believe that waiting for the end of the expression
involves the chronology encoded in the expression tree.

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