INTGR ADDSUB

MODE in INTEGER range 0 to I ANSWER out INTEGER range -8 to 7) end INTGR.ADDSUB ... 

Like the INTGR ADDSUB example in Figure 6.2, the whole architectural description would be s3mthesized as the compiler does not know which features or functions within the component will be used by a particular design. This is therefore a bad approach if the component must implement a flexible selectable function. 

The same table shows the data for the INTGR ADDSUB-DATAFLOW model. This is an integer addition or subtraction circuit, the function of which is selected by the MODE input signal. As the statistics indicate, the s)mthesized circuit occupies almost three times the area as tiie single adder circuit. This consists of three elements ... 

In the final architecture that uses the user-defined ripple-cany function both addition and subtraction are possible. SIGNED ADDSUB contains a call to the same RIPPLE function used in RIPPLE3. This time, howevei> the operation is selected externally by the MODE signal and flierefore the full function must be synthesized. This architecture is included so that the circuit can be compared with the integer addition and subtraction architecture, INTGR ADDSUB. 

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