CODEWITHSUNDEEP
conditional-statementsverilogassignconditional-operatorhdl
user14173380
user14173380

Reputation:

Verilog: More efficient way to use ternary operator

I have written the following assign statement:

assign F = (BCD == 4'd1 | BCD == 4'd2 | BCD == 4'd3 | BCD == 4'd4 | BCD == 4'd5) ? 1'b1 : 1'b0;

where if the BCD input (4-bits) is 1-5, the function returns a 1 and otherwise returns a 0. This works perfectly how I intended, but I'm looking for a more efficient way to write the "OR" parts. Is there a more efficient way to write this?

Upvotes: 0

Views: 3958

Answers (4)

m4j0rt0m
m4j0rt0m

Reputation: 354

There are several ways to do this:

a) Boundary check.

assign F = (BCD > 4'd0) & (BCD < 4'd6);

b) OR reduction and a high limit check.

assign F = |BCD & (BCD < 4'd6);

c) This is a behavioural hardware description, it would be optimized by the synthesis tool. It is parameterized, though.

localparam LOW = 1;
localparam HIGH = 5;
integer i;
reg F;
always @ (*) begin
  F = 1'b0;
  for(i = LOW; i <= HIGH; i = i + 1) begin: val_check
    if(BCD == i[3:0]) F = 1'b1;
  end
end

Upvotes: 0

dave_59
dave_59

Reputation: 42698

There's no need for the ternary operator here. The result of each equality(==) is 1-bit, and you are doing a bit-wise OR (|). You probably should be using a logical OR (||) whose result is also 1-bit.

assign F = (BCD == 4'd1 || BCD == 4'd2 || BCD == 4'd3 || BCD == 4'd4 || BCD == 4'd5);

In SystemVerilog which most tools are supporting, you can use the inside operator

assign F = BCD inside {[1:5]}; //  contiguous range
assign F = BCD inside {[1:3],5, [7:10]}; //  noncontiguous values

Upvotes: 3

Light
Light

Reputation: 1316

No, one should use each complete expressions separated by |. However, in this particular situation, you can use (BCD >= 4'd1) & (BCD <= 4'd5).

Upvotes: 2

toolic
toolic

Reputation: 62163

Since your values are in a continuous range, this can be simplified as:

assign F = ((BCD >= 4'd1) && (BCD <= 4'd5));

If your tool set supports SystemVerilog syntax, you could also use the inside operator. Refer to IEEE Std 1800-2017, section 11.4.13 Set membership operator.

Upvotes: 1

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