optimize mload instruction to not allocate a temporary vector

core/src/eval/misc.rs

@@ -81,7 +81,7 @@ pub fn mload(state: &mut Machine) -> Control {
 	pop_u256!(state, index);
 	try_or_fail!(state.memory.resize_offset(index, U256::from(32)));
 	let index = as_usize_or_fail!(index);
-	let value = H256::from_slice(&state.memory.get(index, 32)[..]);
+	let value = state.memory.get_h256(index);
 	push!(state, value);
 	Control::Continue(1)
 }

core/src/memory.rs

@@ -2,7 +2,7 @@ use crate::{ExitError, ExitFatal};
 use alloc::vec::Vec;
 use core::cmp::min;
 use core::ops::{BitAnd, Not};
-use primitive_types::U256;
+use primitive_types::{H256, U256};
 
 /// A sequencial memory. It uses Rust's `Vec` for internal
 /// representation.
@@ -82,18 +82,27 @@ impl Memory {
 	pub fn get(&self, offset: usize, size: usize) -> Vec<u8> {
 		let mut ret = Vec::new();
 		ret.resize(size, 0);
+		self.get_to(offset, &mut ret);
+		ret
+	}
+
+	/// Get `H256` from a specific offset in memory.
+	pub fn get_h256(&self, offset: usize) -> H256 {
+		let mut ret = [0; 32];
+		self.get_to(offset, &mut ret);
+		H256(ret)
+	}
 
+	fn get_to(&self, offset: usize, buf: &mut [u8]) {
 		#[allow(clippy::needless_range_loop)]
-		for index in 0..size {
+		for index in 0..buf.len() {
 			let position = offset + index;
 			if position >= self.data.len() {
 				break;
 			}
 
-			ret[index] = self.data[position];
+			buf[index] = self.data[position];
 		}
-
-		ret
 	}
 
 	/// Set memory region at given offset. The offset and value is considered