Source

Turn Off Rightmost 1 Bit

Credit: Hacker's Delight, Section 2-1: Manipulating Rightmost Bits

Use the following formula to turn off the rightmost 1-bit in a word, producing 0 if none (e.g., 01011000 -> 01010000)

This can be used to determine if an unsigned integer is a power of 2 or is 0: apply the formula followed by a 0-test on the result.

module Turn_Off_Rightmost_1_Bit
#(
    parameter WORD_WIDTH = 0
)
(
    input   wire    [WORD_WIDTH-1:0]    word_in,
    output  reg     [WORD_WIDTH-1:0]    word_out
);

    initial begin
        word_out = {WORD_WIDTH{1'b0}};
    end

    localparam ONE = {{WORD_WIDTH-1{1'b0}},1'b1};

    always @(*) begin
        word_out = word_in & (word_in - ONE);
    end

endmodule

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