The Essentials ofComputer(computer) 458

# The Essentials ofComputer(computer) 458 - j N j j True 1...

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N * True j > 1 False K K K Program complete –1 j j j j 1 FIGURE 9.12 Data Flow Graph Corresponding to the Program to Calculate N ! The corresponding data flow graph is shown in Figure 9.12. The two values, N and 1, are fed into the graph. N becomes token j . When j is compared to 1, if it is greater than 1, the j token is passed through and doubled, with one copy of the token passed to the “–1 node” and one copy passed to the multiply node. If j is not greater than 1, the value of k is passed through as the output of the program. The multiply node can only fire when both a new j token and a new k token are available. The “right facing” triangles that N and 1 feed into are “merge” nodes and fire whenever either input is available. Once N and 1 are fed into the graph, they are “used up” and the new j and new k values cause the merge nodes to fire. Al Davis, of the University of Utah, built the first dataflow machine in 1977.
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