util.indexedbheap: Fix heap datastructure corruption in :reschedule(smaller_value)

spec/util_indexedbheap_spec.lua

@@ -0,0 +1,33 @@
+local ibh = require"util.indexedbheap";
+
+local function verify_heap_property(priorities)
+	for k in ipairs(priorities) do
+		local parent = priorities[k];
+		local childA = priorities[2*k];
+		local childB = priorities[2*k+1];
+		-- print("-", parent, childA, childB)
+		assert(childA == nil or childA > parent, "heap property violated");
+		assert(childB == nil or childB > parent, "heap property violated");
+	end
+end
+
+local h
+setup(function ()
+	h = ibh.create();
+end)
+describe("util.indexedbheap", function ()
+	it("item can be moved from end to top", function ()
+		verify_heap_property(h);
+		h:insert("a", 1);
+		verify_heap_property(h);
+		h:insert("b", 2);
+		verify_heap_property(h);
+		h:insert("c", 3);
+		verify_heap_property(h);
+		local id = h:insert("*", 10);
+		verify_heap_property(h);
+		h:reprioritize(id, 0);
+		verify_heap_property(h);
+		assert.same({ 0, "*", id }, { h:pop() });
+	end)
+end);

util/indexedbheap.lua

@@ -23,7 +23,7 @@ local function _percolate_up(self, k, sync, index)
 	local tmp_sync = sync[k];
 	while k ~= 1 do
 		local parent = math_floor(k/2);
-		if tmp < self[parent] then break; end
+		if tmp >= self[parent] then break; end
 		self[k] = self[parent];
 		sync[k] = sync[parent];
 		index[sync[k]] = k;