Redesign BlockCache's age tracking to run in constant time

Speeds up spectrum painting by 40-90% depending on how much of the audio
data is being read from the cache.

Originally committed to SVN as r6488.

aegisub/src/block_cache.h

@@ -37,6 +37,7 @@
 
 #ifndef AGI_PRE
 #include <algorithm>
+#include <list>
 #include <vector>
 #endif
 
@@ -103,8 +104,10 @@ class DataBlockCache {
 
 	/// DOCME
 	struct MacroBlock {
-		/// How long has it been since this macroblock was accessed?
-		int age;
+		/// This macroblock's position in the age list
+		/// Is valid iff blocks.size() > 0
+		typename std::list<MacroBlock*>::iterator position;
+
 		/// The blocks contained in the macroblock
 		BlockArray blocks;
 	};
@@ -115,6 +118,12 @@ class DataBlockCache {
 	/// The data in the cache
 	MacroBlockArray data;
 
+	/// Type of a list of macro blocks
+	typedef std::list<MacroBlock*> AgeList;
+
+	/// The data sorted by how long it's been since they were used
+	AgeList age;
+
 	/// Number of blocks per macroblock
 	size_t macroblock_size;
 
@@ -124,13 +133,13 @@ class DataBlockCache {
 	/// Factory object for blocks
 	BlockFactoryT factory;
 
-	/// Used in sorting the macroblocks by age
-	static bool comp_age(const MacroBlock *lft, const MacroBlock *rgt) { return lft->age < rgt->age; }
-
 	/// @brief Dispose of all blocks in a macroblock and mark it empty
 	/// @param mb_index Index of macroblock to clear
 	void KillMacroBlock(MacroBlock &mb)
 	{
+		if (mb.blocks.empty())
+			return;
+
 		for (size_t bi = 0; bi < mb.blocks.size(); ++bi)
 		{
 			BlockT *b = mb.blocks[bi];
@@ -139,6 +148,7 @@ class DataBlockCache {
 		}
 
 		mb.blocks.clear();
+		age.erase(mb.position);
 	}
 
 public:
@@ -204,30 +214,19 @@ public:
 			return;
 		}
 
-		// Get a list of macro blocks sorted by access count
-		std::vector<MacroBlock*> access_data;
-		access_data.reserve(data.size());
-		// For whatever reason, G++ pukes if I try using iterators here...
-		for (size_t mbi = 0; mbi != data.size(); ++mbi)
-		{
-			if (data[mbi].blocks.size())
-				access_data.push_back(&data[mbi]);
-		}
-		sort(access_data.begin(), access_data.end(), comp_age);
-
 		// Sum up data size until we hit the max
 		size_t cur_size = 0;
 		size_t block_size = factory.GetBlockSize();
-		size_t mbi = 0;
-		for (; mbi < access_data.size() && cur_size < max_size; ++mbi)
+		typename AgeList::iterator it = age.begin();
+		for (; it != age.end() && cur_size < max_size; ++it)
 		{
-			BlockArray &ba = access_data[mbi]->blocks;
+			BlockArray &ba = (*it)->blocks;
 			cur_size += (ba.size() - std::count(ba.begin(), ba.end(), (BlockT*)0)) * block_size;
 		}
 		// Hit max, clear all remaining blocks
-		for (++mbi; mbi < access_data.size(); ++mbi)
+		for (; it != age.end(); ++it)
 		{
-			KillMacroBlock(*access_data[mbi]);
+			KillMacroBlock(**it);
 		}
 	}
 
@@ -243,19 +242,20 @@ public:
 		size_t mbi = i >> MacroblockExponent;
 		assert(mbi < data.size());
 
-		// Age all of the other macroblocks
-		for (size_t idx = 0; idx < data.size(); ++idx)
-		{
-			data[idx].age += 1;
-		}
-
 		MacroBlock &mb = data[mbi];
-		mb.age = 0;
 
 		if (mb.blocks.size() == 0)
 		{
 			mb.blocks.resize(macroblock_size);
 		}
+		else
+		{
+			age.erase(mb.position);
+		}
+
+		// Move this macroblock to the front of the age list
+		age.push_front(&mb);
+		mb.position = age.begin();
 
 		size_t block_index = i & macroblock_index_mask;
 		assert(block_index < mb.blocks.size());