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authorWaqas Hussain <waqas20@gmail.com>2013-10-30 17:30:35 -0400
committerWaqas Hussain <waqas20@gmail.com>2013-10-30 17:30:35 -0400
commit511f7a76a11199b7cd4d13c85f0703f3e7930e3c (patch)
treeb5df634d73656d26232ba4714534e4a5c7ca3298 /util
parent75aefae1a9bf676ddf59d571ba0e55098298509f (diff)
downloadprosody-511f7a76a11199b7cd4d13c85f0703f3e7930e3c.tar.gz
prosody-511f7a76a11199b7cd4d13c85f0703f3e7930e3c.zip
util.indexedbheap: A priority queue implementation with a reverse index with no per-entry memory allocation.
Diffstat (limited to 'util')
-rw-r--r--util/indexedbheap.lua153
1 files changed, 153 insertions, 0 deletions
diff --git a/util/indexedbheap.lua b/util/indexedbheap.lua
new file mode 100644
index 00000000..3cb03037
--- /dev/null
+++ b/util/indexedbheap.lua
@@ -0,0 +1,153 @@
+
+local setmetatable = setmetatable;
+local math_floor = math.floor;
+local t_remove = table.remove;
+
+local function _heap_insert(self, item, sync, item2, index)
+ local pos = #self + 1;
+ while true do
+ local half_pos = math_floor(pos / 2);
+ if half_pos == 0 or item > self[half_pos] then break; end
+ self[pos] = self[half_pos];
+ sync[pos] = sync[half_pos];
+ index[sync[pos]] = pos;
+ pos = half_pos;
+ end
+ self[pos] = item;
+ sync[pos] = item2;
+ index[item2] = pos;
+end
+
+local function _percolate_up(self, k, sync, index)
+ local tmp = self[k];
+ local tmp_sync = sync[k];
+ while k ~= 1 do
+ local parent = math_floor(k/2);
+ if tmp < self[parent] then break; end
+ self[k] = self[parent];
+ sync[k] = sync[parent];
+ index[sync[k]] = k;
+ k = parent;
+ end
+ self[k] = tmp;
+ sync[k] = tmp_sync;
+ index[tmp_sync] = k;
+ return k;
+end
+
+local function _percolate_down(self, k, sync, index)
+ local tmp = self[k];
+ local tmp_sync = sync[k];
+ local size = #self;
+ local child = 2*k;
+ while 2*k <= size do
+ if child ~= size and self[child] > self[child + 1] then
+ child = child + 1;
+ end
+ if tmp > self[child] then
+ self[k] = self[child];
+ sync[k] = sync[child];
+ index[sync[k]] = k;
+ else
+ break;
+ end
+
+ k = child;
+ child = 2*k;
+ end
+ self[k] = tmp;
+ sync[k] = tmp_sync;
+ index[tmp_sync] = k;
+ return k;
+end
+
+local function _heap_pop(self, sync, index)
+ local size = #self;
+ if size == 0 then return nil; end
+
+ local result = self[1];
+ local result_sync = sync[1];
+ index[result_sync] = nil;
+ if size == 1 then
+ self[1] = nil;
+ sync[1] = nil;
+ return result, result_sync;
+ end
+ self[1] = t_remove(self);
+ sync[1] = t_remove(sync);
+ index[sync[1]] = 1;
+
+ _percolate_down(self, 1, sync, index);
+
+ return result, result_sync;
+end
+
+local indexed_heap = {};
+
+function indexed_heap:insert(item, priority, id)
+ if id == nil then
+ id = self.current_id;
+ self.current_id = id + 1;
+ end
+ self.items[id] = item;
+ _heap_insert(self.priorities, priority, self.ids, id, self.index);
+ return id;
+end
+function indexed_heap:pop()
+ local priority, id = _heap_pop(self.priorities, self.ids, self.index);
+ if id then
+ local item = self.items[id];
+ self.items[id] = nil;
+ return priority, item, id;
+ end
+end
+function indexed_heap:peek()
+ return self.priorities[1];
+end
+function indexed_heap:reprioritize(id, priority)
+ local k = self.index[id];
+ if k == nil then return; end
+ self.priorities[k] = priority;
+
+ k = _percolate_up(self.priorities, k, self.ids, self.index);
+ k = _percolate_down(self.priorities, k, self.ids, self.index);
+end
+function indexed_heap:remove_index(k)
+ local size = #self.priorities;
+
+ local result = self.priorities[k];
+ local result_sync = self.ids[k];
+ local item = self.items[result_sync];
+ if result == nil then return; end
+ self.index[result_sync] = nil;
+ self.items[result_sync] = nil;
+
+ self.priorities[k] = self.priorities[size];
+ self.ids[k] = self.ids[size];
+ self.index[self.ids[k]] = k;
+ t_remove(self.priorities);
+ t_remove(self.ids);
+
+ k = _percolate_up(self.priorities, k, self.ids, self.index);
+ k = _percolate_down(self.priorities, k, self.ids, self.index);
+
+ return result, item, result_sync;
+end
+function indexed_heap:remove(id)
+ return self:remove_index(self.index[id]);
+end
+
+local mt = { __index = indexed_heap };
+
+local _M = {
+ create = function()
+ return setmetatable({
+ ids = {}; -- heap of ids, sync'd with priorities
+ items = {}; -- map id->items
+ priorities = {}; -- heap of priorities
+ index = {}; -- map of id->index of id in ids
+ current_id = 1.5
+ }, mt);
+ end
+};
+return _M;