Added (very) crude Collatz conjecture module.

1 files changed, 57 insertions, 0 deletions

diff --git a/collatz.v b/collatz.v
new file mode 100644
index 0000000..e90c1bd
--- /dev/null
+++ b/collatz.v
@@ -0,0 +1,57 @@
+module collatz (
+  input clk,
+  input rst,
+
+  input wire [15:0] in_start,
+  input wire start_int,
+
+  output reg [15:0] o_count,
+  output finish_int
+);
+
+  localparam IDLE = 0;
+  localparam SPINNING = 1;
+  localparam WAIT_TICK = 2;
+
+  reg [1:0] state = 0;
+  reg [15:0] count = 0;
+  reg [15:0] n = 0;
+
+  wire is_even;
+
+  assign is_even = ~n[0]; 
+  assign finish_int = (n == 1 && state == IDLE);
+
+  always @(posedge start_int) begin
+    if (state == IDLE) begin
+      state <= SPINNING;
+      n <= in_start;
+    end
+  end
+
+  always @(posedge clk or posedge rst) begin
+    if (rst == 1'b1) begin
+      state <= IDLE;
+      count <= 0;
+      n <= 0;
+    end else if (state == IDLE) begin
+      n <= 0;
+    end else if (state == SPINNING) begin
+      if (n <= 1) begin
+        o_count = count;
+        state = WAIT_TICK;
+        // finish_int should be triggered.
+      end else begin
+        if (is_even) begin
+          n <= n >> 1;
+        end else begin
+          n <= n * 3 + 1;
+        end
+        count <= count + 1;
+      end
+    end else if (state == WAIT_TICK) begin
+      state <= IDLE;
+    end
+  end
+
+  endmodule