Credit: Hacker's Delight, Section 2-1: Manipulating Rightmost Bits
Use one of the following formulas to create a word with 1’s at the positions of the trailing 0’s in the input, and 0’s elsewhere, producing 0 if none (e.g., 01011000 -> 00000111)
`default_nettype none
module Bitmask_Turn_On_Trailing_0_Bits
#(
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