Verilog code to implement a 4-bit magnitude comparator circuit.

Here’s an example Verilog code to implement a 4-bit magnitude comparator circuit:

module magnitude_comparator(
  input [3:0] A,
  input [3:0] B,
  output reg EQ,
  output reg GT,
  output reg LT
);

  always @(A, B) begin
    if (A == B) begin
      EQ = 1;
      GT = 0;
      LT = 0;
    end else if (A > B) begin
      EQ = 0;
      GT = 1;
      LT = 0;
    end else begin
      EQ = 0;
      GT = 0;
      LT = 1;
    end
  end
  
endmodule

In this Verilog code, the `magnitude_comparator` module takes two 4-bit inputs `A` and `B`, and outputs three 1-bit signals `EQ`, `GT`, and `LT`. The output signals correspond to the three possible outcomes of comparing the magnitudes of `A` and `B`: equal, greater than, or less than.

The `always` block is triggered whenever there is a change in the values of `A` and `B`. The block compares the magnitudes of `A` and `B` using a series of if-else statements, and sets the output signals accordingly.

Note that in this implementation, the output signals are declared as reg types, which are used for output signals that are updated in an `always` block.

This is just one example implementation of a 4-bit magnitude comparator circuit in Verilog. There are many other ways to implement a comparator, depending on the specific requirements of the design.