paralell assignment problem

[skaller <skaller@users.sourceforge.net>]

Does anyone know how to solve the parallel assignment problem?
Name invented by me to describe this problem:

x1,x2,x3..xn = e1,e2,e3 .. en

where ei might contain the variables xj. (Note = here is assignment).

The solution is a sequence of assignments involving
only xi, ei, and ti, where ti are temporaries introduced
to save the values of the expressions. For example,
a solution to

	x,y = y,x

is

	t = x; x = y; y = t

I seek a solution which minimises the number of assignments.
Note that the relation 

	i < j == ej doesn't depend on xi

is not transitive. This (a) confuses me enough I can't
see the solution, and (b) is precisely what allows
a temporary to remove a dependence.


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John Skaller, mailto:skaller@users.sf.net
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