paralell assignment problem
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Date:  20050209 (11:19) 
From:  Radu Grigore <radugrigore@g...> 
Subject:  Re: [Camllist] Re: paralell assignment problem 
On Wed, 9 Feb 2005 11:43:34 +0200, Radu Grigore <radugrigore@gmail.com> wrote: > 1. hold the original value of a variable > 2. hold the result of an expression and write it later to the destination > > Point (1) requires one extra assignment, while point (2) requires two > extra assignments. The effect is however the same: one of the > variable's value can be computed as soon as desired. Therefore we will > only use (1). [NOTE that your approach used (2) and hence is clearly > suboptimal]. One more mistake. Both approaches introduce _one_ extra assignment and the algorithm described subsequently is independent on the choice of (1) or (2). For the problem: a = b+c b = c c = a+b The algorithm says: introduce a temporary for c, and the order is c, a, b. With choice (1) the solution is the one I already wrote. With choice (2) it is: // compute temporaries t = a+b // compute c, a, b (skip c because we have temporary, this is what I missed) a = b+c b = c // use temporaries c = t ... for a total of 4 assignments (same as with choice 1). This is better than the 5 assignments given by your algorithm and it does NOT depend on breaking the rule about using temporaries only to save results of expressions (but not initial values).  regards, radu http://rgrig.idilis.ro/