Altera Nios II C2H Compiler Manual do Utilizador descarregar pdf (Página 85)

Altera Corporation 9.1 3–45

November 2009 Nios II C2H Compiler User Guide

C-to-Hardware Mapping Reference

Figure 3–22 shows the dependency graph for the do loop in

Example 3–36, which has loop-carried dependencies.

Example 3–36. Loop-Carried Dependency

int simple_hash(int *data, int len)

{

int hash = 0;

{

int data_word = *data++;

hash = hash + data_word;

hash = hash ^ data_word;

} while (len--);

return hash;

}

Figure 3–22. Loop-Carried Dependency

Variables data and hash have loop-carried dependencies, illustrated by

the cyclic arrows in Figure 3–22. The arrow for hash indicates that the

calculation on State 1 in iteration N is dependent on the result of the

calculation from State 2 in iteration (N-1). The arrow for data in State 0

illustrates the ideal case in which a state depends only on its own output.

The ideal case does not restrict the scheduling of successive iterations.

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