Optimized memory usage

Author: arkpar

ethcore/src/evm/interpreter/memory.rs

@@ -16,7 +16,8 @@
 
 use util::U256;
 use evm::ReturnData;
-use std::cmp::min;
+
+const MAX_RETURN_WASTE_BYTES: usize = 16384;
 
 pub trait Memory {
 	/// Retrieve current size of the memory
@@ -39,7 +40,7 @@ pub trait Memory {
 	fn writeable_slice(&mut self, offset: U256, size: U256) -> &mut[u8];
 	fn dump(&self);
 	/// Convert memory into return data.
-	fn into_return_data(self, offset: usize, size: usize) -> ReturnData;
+	fn into_return_data(self, offset: U256, size: U256) -> ReturnData;
 }
 
 /// Checks whether offset and size is valid memory range
@@ -114,10 +115,18 @@ impl Memory for Vec<u8> {
 		}
 	}
 
-	fn into_return_data(self, offset: usize, size: usize) -> ReturnData {
-		let offset = min(offset, self.len());
-		let size = min(size, self.len() - offset);
-		ReturnData::new(self, offset, size)
+	fn into_return_data(mut self, offset: U256, size: U256) -> ReturnData {
+		let offset = offset.low_u64() as usize;
+		let size = size.low_u64() as usize;
+		if !is_valid_range(offset, size) {
+			return ReturnData::empty()
+		}
+		if self.len() - size > MAX_RETURN_WASTE_BYTES {
+			let mem = self.drain(offset..).take(size).collect();
+			ReturnData::new(mem, 0, size)
+		} else {
+			ReturnData::new(self, offset, size)
+		}
 	}
 }
 

ethcore/src/evm/interpreter/mod.rs

@@ -170,7 +170,7 @@ impl<Cost: CostType> evm::Evm for Interpreter<Cost> {
 					let mem = mem::replace(&mut self.mem, Vec::new());
 					return Ok(GasLeft::NeedsReturn {
 						gas_left: gas.as_u256(),
-						data: mem.into_return_data(usize::from_u256(init_off)?, usize::from_u256(init_size)?),
+						data: mem.into_return_data(init_off, init_size),
 						apply_state: apply
 					});
 				},
@@ -499,6 +499,9 @@ impl<Cost: CostType> Interpreter<Cost> {
 			instructions::CODESIZE => {
 				stack.push(U256::from(code.len()));
 			},
+			instructions::RETURNDATASIZE => {
+				stack.push(U256::from(self.return_data.len()))
+			},
 			instructions::EXTCODESIZE => {
 				let address = u256_to_address(&stack.pop_back());
 				let len = ext.extcodesize(&address)?;