63 lines
1.3 KiB
Lua
63 lines
1.3 KiB
Lua
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-- a simple first-in-first-out queue
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-- very similar to the one in https://github.com/minetest/minetest/pull/7683
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local fifo_queue = {}
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local metatable = {__index = fifo_queue}
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-- creates a new empty queue
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function fifo_queue.new()
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local q = {n_in = 0, n_out = 0, i_out = 1, buf_in = {}, buf_out = {}}
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setmetatable(q, metatable)
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return q
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end
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-- adds an element to the queue
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function fifo_queue.add(self, v)
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local n = self.n_in + 1
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self.n_in = n
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self.buf_in[n] = v
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end
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-- removes and returns the next element, or nil of empty
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function fifo_queue.take(self)
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local i_out = self.i_out
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if i_out <= self.n_out then
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local v = self.buf_out[i_out]
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self.i_out = i_out + 1
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self.buf_out[i_out] = true
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return v
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end
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-- buf_out is empty, try to swap
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self.i_out = 1
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self.n_out = 0
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if self.n_in == 0 then
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return nil -- empty
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end
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-- swap
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self.n_out = self.n_in
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self.n_in = 0
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self.buf_out, self.buf_in = self.buf_in, self.buf_out
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local v = self.buf_out[1]
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self.i_out = 2
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self.buf_out[1] = true
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return v
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end
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-- returns whether the queue is empty
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function fifo_queue.is_empty(self)
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return self.n_out == self.i_out + 1 and self.n_in == 0
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end
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-- returns stuff for iteration in a for loop, like pairs
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-- adding new elements while iterating is no problem
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function fifo_queue.iter(self)
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return fifo_queue.take, self, nil
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end
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return fifo_queue
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