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change order of statements and make gender neutral

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matt venn 2020-04-22 17:54:39 +02:00
parent a4885ce494
commit 9d69f8a518
1 changed files with 17 additions and 16 deletions
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33
docs/examples/puzzles/wolf_goat_cabbage.sv
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@ -1,38 +1,39 @@
// A man needs to cross a river with a wolf, a goat and a cabbage. His boat is only large
// enough to carry himself and one of his three possessions, so he must transport these
// items one at a time. However, if he leaves the wolf and the goat together unattended,
// then the wolf will eat the goat; similarly, if he leaves the goat and the cabbage together
// unattended, then the goat will eat the cabbage. How can the man get across safely with
// his three items?
// A person needs to cross a river with a wolf, a goat and a cabbage. Their boat is only large
// enough to carry themselves and one of their three possessions, so they must transport these
// items one at a time. However, if they leave the wolf and the goat together unattended,
// then the wolf will eat the goat; similarly, if they leave the goat and the cabbage together
// unattended, then the goat will eat the cabbage. How can the person get across safely with
// their three items?
module wolf_goat_cabbage (input clk, input w, g, c);
// everyone starts at the 1st river bank
reg bank_w = 0; // wolf
reg bank_g = 0; // goat
reg bank_c = 0; // cabbage
reg bank_m = 0; // man
reg bank_person = 0; // person who drives the boat
always @(posedge clk) begin
// person travels and takes the selected item with him
if (w && (bank_w == bank_person)) bank_w <= !bank_person;
if (g && (bank_g == bank_person)) bank_g <= !bank_person;
if (c && (bank_c == bank_person)) bank_c <= !bank_person;
bank_person <= !bank_person;
// maximum one of the control signals must be high
assume (w+g+c <= 1);
// we want wolf, goat, and cabbage on the 2nd river bank
cover (bank_w && bank_g && bank_c);
// write a cover statement that will result in the desired combination
cover(bank_w == 1 && bank_g == 1 && bank_c == 1);
// don't leave wolf and goat unattended
if (bank_w != bank_m) begin
if (bank_w != bank_person) begin
assume (bank_w != bank_g);
end
// don't leave goat and cabbage unattended
if (bank_g != bank_m) begin
if (bank_g != bank_person) begin
assume (bank_g != bank_c);
end
// man travels and takes the selected item with him
if (w && (bank_w == bank_m)) bank_w <= !bank_m;
if (g && (bank_g == bank_m)) bank_g <= !bank_m;
if (c && (bank_c == bank_m)) bank_c <= !bank_m;
bank_m <= !bank_m;
end
endmodule