RC ADDER

The adder itself is a procedure called RC ADDER contained in the package ARITH UTILS. This is accessed as usual through a Use clause. 

The architecture contains a single concurrent call to the RC ADDER procedure. The size of the adder is defined by the size of the array types widiin the call. RCOUT and OVERFLOW contain the current sum and carry results for the adder. These values are then used by the irregular Generate statement, introduced in Chapter 5, to construct the actual adder result. Three different types of bit are produced - the sign, the radix and the ordinary bits. In each case, the logic is complicated by the overflow detection, saturation and comparison logic. The actual functions are not very important. 

The adder itself is contained in Figure 8.13. The ARITH UTILS package contains the two procedures RC ADDER and FULL ADDER. The first defines an N-bit ripple-carry adder and the second a single-bit full adder procedure. These procedures are similar to fiiose constructed as functions... 

RC ADDER(ABUS, BBUS, SUB, RCOUT, OVERFLOW) OUTPUT LOGIC for K in IS downto 0generate... 

OVER <= CARRY(A left+l) xor CARRY(A1eft) end RC ADDER ... 

As before, the adder types are separated into three sections - Integer, RC and CLA Within each section both the s3mthesis and optimization results will be discussed together. 

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