Processor Description Languages

8.6 Language Constructs for Efficient Hardware Implementation 203

is to encapsulate the computation for modular code development. The following

example demonstrates the use of shared functions for the

ADD and SUB instruction

of Section 8.6.1.

function [31:0] addsub([31:0]in0, [31:0]in1, cin) shared {

assign addsub = TIEadd(in0, in1, cin);

}

operation ADD {out AR res, in AR input0, in AR input1 } {

assign res = addsub(input0, input1, 1’b0);

}

operation SUB {out AR res, in AR input0, in AR input1 } {

assign res = addsub(input0, ∼ input1, 1’b1);

}

Instead of writing a semantic for the two instructions to share the 32-bit adder,

the adder is encapsulated in a