Add experimental, disabled XOR mode, leaving all compression to ZSTD.…

… Seems to perform worse.
hrydgard · Feb 13, 2023 · 83e13a4 · 83e13a4
1 parent 1dfda22
commit 83e13a4
Showing 1 changed file with 58 additions and 31 deletions.
diff --git a/Core/SaveState.cpp b/Core/SaveState.cpp
@@ -102,9 +102,14 @@ namespace SaveState
 	}
 
 	struct StateBuffer {
+		void Clear() {
+			zstd_compressed.clear();
+			decompressed_size = 0;
+			compressed_size = 0;
+		}
 		std::vector<u8> zstd_compressed;
-		size_t decompressed_size;
-		size_t compressed_size;
+		size_t decompressed_size = 0;
+		size_t compressed_size = 0;
 	};
 
 	// This ring buffer of states is for rewind save states, which are kept in RAM.
@@ -190,6 +195,8 @@ namespace SaveState
 			});
 		}
 
+		const bool USE_XOR = false;
+
 		void Compress(StateBuffer *result, std::vector<u8> &state, const std::vector<u8> &base)
 		{
 			std::lock_guard<std::mutex> guard(lock_);
@@ -199,26 +206,36 @@ namespace SaveState
 
 			double start_time = time_now_d();
 			std::vector<u8> compressed;
-			compressed.reserve(512 * 1024);
-			for (size_t i = 0; i < state.size(); i += BLOCK_SIZE)
-			{
-				int blockSize = std::min(BLOCK_SIZE, (int)(state.size() - i));
-				if (i + blockSize > base.size() || memcmp(&state[i], &base[i], blockSize) != 0)
+			if (USE_XOR) {
+				compressed.resize(state.size());
+				for (size_t i = 0; i < state.size(); i++) {
+					if (i >= base.size()) {
+						compressed[i] = state[i];
+					} else {
+						compressed[i] = base[i] ^ state[i];
+					}
+				}
+			} else {
+				compressed.reserve(512 * 1024);
+				for (size_t i = 0; i < state.size(); i += BLOCK_SIZE)
 				{
-					compressed.push_back(1);
-					compressed.insert(compressed.end(), state.begin() + i, state.begin() + i + blockSize);
+					int blockSize = std::min(BLOCK_SIZE, (int)(state.size() - i));
+					if (i + blockSize > base.size() || memcmp(&state[i], &base[i], blockSize) != 0)
+					{
+						compressed.push_back(1);
+						compressed.insert(compressed.end(), state.begin() + i, state.begin() + i + blockSize);
+					} else {
+						compressed.push_back(0);
+					}
 				}
-				else
-					compressed.push_back(0);
 			}
 
 			double taken_s = time_now_d() - start_time;
 			DEBUG_LOG(SAVESTATE, "Rewind: Compressed save from %d bytes to %d in %0.2f ms.", (int)state.size(), (int)compressed.size(), taken_s * 1000.0);
 
-			// Temporarily allocate a buffer to do decompression in.
+			// Temporarily allocate a buffer to do compression in.
 			size_t compressCapacity = ZSTD_compressBound(compressed.size());
 			u8 *compress_buf = (u8 *)malloc(compressCapacity);
-
 			result->compressed_size = ZSTD_compress(compress_buf, compressCapacity, compressed.data(), compressed.size(), 0);
 			if (result->compressed_size) {
 				result->zstd_compressed = std::vector<u8>(result->compressed_size, 0);
@@ -241,25 +258,35 @@ namespace SaveState
 			std::vector<u8> compressed = std::vector<u8>(buffer.decompressed_size, 0);
 			ZSTD_decompress(&compressed[0], compressed.size(), buffer.zstd_compressed.data(), buffer.zstd_compressed.size());
 
-			for (size_t i = 0; i < compressed.size(); )
-			{
-				if (compressed[i] == 0)
-				{
-					++i;
-					int blockSize = std::min(BLOCK_SIZE, (int)(base.size() - result.size()));
-					result.insert(result.end(), basePos, basePos + blockSize);
-					basePos += blockSize;
+			if (USE_XOR) {
+				result.resize(compressed.size());
+				for (size_t i = 0; i < compressed.size(); i++) {
+					if (i < base.size()) {
+						result[i] = compressed[i] ^ base[i];
+					} else {
+						result[i] = compressed[i];
+					}
 				}
-				else
-				{
-					++i;
-					int blockSize = std::min(BLOCK_SIZE, (int)(compressed.size() - i));
-					result.insert(result.end(), compressed.begin() + i, compressed.begin() + i + blockSize);
-					i += blockSize;
-					// This check is to avoid advancing basePos out of range, which MSVC catches.
-					// When this happens, we're at the end of decoding anyway.
-					if (base.end() - basePos >= blockSize) {
+			} else {
+				for (size_t i = 0; i < compressed.size(); ) {
+					if (compressed[i] == 0) {
+						++i;
+						int blockSize = std::min(BLOCK_SIZE, (int)(base.size() - result.size()));
+						_dbg_assert_(blockSize >= 0);
+						result.insert(result.end(), basePos, basePos + blockSize);
 						basePos += blockSize;
+					} else {
+						++i;
+						int blockSize = std::min(BLOCK_SIZE, (int)(compressed.size() - i));
+						if (blockSize > 0) {
+							result.insert(result.end(), compressed.begin() + i, compressed.begin() + i + blockSize);
+							i += blockSize;
+							// This check is to avoid advancing basePos out of range, which MSVC catches.
+							// When this happens, we're at the end of decoding anyway.
+							if (base.end() - basePos >= blockSize) {
+								basePos += blockSize;
+							}
+						}
 					}
 				}
 			}
@@ -280,7 +307,7 @@ namespace SaveState
 			baseMapping_.clear();
 			baseMapping_.resize(size_);
 			for (auto &s : states_) {
-				s.clear();
+				s.Clear();
 			}
 			buffer_.clear();
 			base_ = -1;