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Add "pour_853_4" puzzle to examples

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Signed-off-by: Clifford Wolf <clifford@clifford.at>
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Clifford Wolf 2018-08-25 18:21:34 +02:00
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docs/examples/puzzles/pour_853_to_4.sv Normal file
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// You are given an 8 litre bucket of water, and two empty buckets which can
// contain 5 and 3 litre respectively. You are required to divide the water into
// two by pouring water between buckets (that is, to end up with 4 litre in the 8
// litre bucket, and 4 litre in the 5 litre bucket).
//
// Inspired by:
// https://github.com/DennisYurichev/random_notes/blob/master/Z3/pour.py
module pour_853_to_4 (
input clk,
input [1:0] src, dst
);
reg [3:0] state [0:2];
reg [3:0] max_amount [0:2];
reg [3:0] xfer_amount;
initial begin
state[0] = 8;
state[1] = 0;
state[2] = 0;
max_amount[0] = 8;
max_amount[1] = 5;
max_amount[2] = 3;
end
always @* begin
assume (src < 3);
assume (dst < 3);
assume (src != dst);
if (state[src] > (max_amount[dst] - state[dst]))
xfer_amount = max_amount[dst] - state[dst];
else
xfer_amount = state[src];
cover (state[0] == 4 && state[1] == 4);
end
always @(posedge clk) begin
state[src] <= state[src] - xfer_amount;
state[dst] <= state[dst] + xfer_amount;
end
endmodule