What does the Verilog localparam X code below mean? From my understanding it is as follows:
if(y==4) X = +64; else if(Y==3) X = +32; else if(Y==2) X = +16; else if(Y==1) X = +8; else if(Y==0) X = +4; else X = +2; Is this correct? If so, another thing that doesn't make sense to me is the '+' after the '=' sign, e.g., (X = +2)? Is this something unique to localparam variables?
localparam X = (Y==4) ? +64 : (Y==3) ? +32 : (Y==2) ? +16 : (Y==1) ? +8 : (Y==0) ? +4 : +2 ; Yes, the localparam statement is logically equivalent to the if/else pseudocode you showed. The statement uses the conditional operator which has precedence like your if/else.
The + signs are unnecessary in the code. The code behaves the same as if they were not there. Perhaps someone copy-and-pasted more complicated code (with expressions like A+2) and forgot to simplify it. A simpler way to write it is:
localparam X = (Y==4) ? 64 : (Y==3) ? 32 : (Y==2) ? 16 : (Y==1) ? 8 : (Y==0) ? 4 : 2 ; The conditional operator ?: is an expression that behaves similar to an if/else conditional branching procedural statement as you observed. It can be used in places where is is not practical to use procedural statements. A parameter/localparam must be assigned using an expression. You could wrap the if/else in a constant function, but the conditional operator is a convenience. If you were making assignments to a variable, a procedural case statement would be much clearer.
The unary + operator has no purpose other than symmetry with the unary - operator. In can make the intent of the code more clear if you have a mix of positive and negative numbers.
+can be omitted. It is not unique tolocalparam, it can be anywhere. \$\endgroup\$+s were added for visual consistency. \$\endgroup\$