From 6f2dbccfc88a6c6bcf5342aa919016611acb4bc0 Mon Sep 17 00:00:00 2001
From: Wei Tang <wei@that.world>
Date: Sun, 1 Aug 2021 05:19:32 +0000
Subject: [PATCH] Replace all usage of U256::from by const for usize::MAX in
 core

---
 core/src/eval/macros.rs | 4 ++--
 core/src/eval/misc.rs   | 2 +-
 core/src/lib.rs         | 4 ++--
 core/src/memory.rs      | 6 +++---
 core/src/utils.rs       | 7 +++++++
 5 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/core/src/eval/macros.rs b/core/src/eval/macros.rs
index 3fd7a9f6e..9d96a5adb 100644
--- a/core/src/eval/macros.rs
+++ b/core/src/eval/macros.rs
@@ -115,7 +115,7 @@ macro_rules! op3_u256_fn {
 
 macro_rules! as_usize_or_fail {
 	( $v:expr ) => {{
-		if $v > U256::from(usize::MAX) {
+		if $v > crate::utils::U256_USIZE_MAX {
 			return Control::Exit(ExitFatal::NotSupported.into());
 		}
 
@@ -123,7 +123,7 @@ macro_rules! as_usize_or_fail {
 	}};
 
 	( $v:expr, $reason:expr ) => {{
-		if $v > U256::from(usize::MAX) {
+		if $v > crate::utils::U256_USIZE_MAX {
 			return Control::Exit($reason.into());
 		}
 
diff --git a/core/src/eval/misc.rs b/core/src/eval/misc.rs
index db9306e48..b5a6e50ff 100644
--- a/core/src/eval/misc.rs
+++ b/core/src/eval/misc.rs
@@ -32,7 +32,7 @@ pub fn calldataload(state: &mut Machine) -> Control {
 	#[allow(clippy::needless_range_loop)]
 	for i in 0..32 {
 		if let Some(p) = index.checked_add(U256::from(i)) {
-			if p <= U256::from(usize::MAX) {
+			if p <= crate::utils::U256_USIZE_MAX {
 				let p = p.as_usize();
 				if p < state.data.len() {
 					load[i] = state.data[p];
diff --git a/core/src/lib.rs b/core/src/lib.rs
index a35ef86f7..300a07900 100644
--- a/core/src/lib.rs
+++ b/core/src/lib.rs
@@ -103,14 +103,14 @@ impl Machine {
 
 	/// Copy and get the return value of the machine, if any.
 	pub fn return_value(&self) -> Vec<u8> {
-		if self.return_range.start > U256::from(usize::MAX) {
+		if self.return_range.start > crate::utils::U256_USIZE_MAX {
 			let mut ret = Vec::new();
 			ret.resize(
 				(self.return_range.end - self.return_range.start).as_usize(),
 				0,
 			);
 			ret
-		} else if self.return_range.end > U256::from(usize::MAX) {
+		} else if self.return_range.end > crate::utils::U256_USIZE_MAX {
 			let mut ret = self.memory.get(
 				self.return_range.start.as_usize(),
 				usize::MAX - self.return_range.start.as_usize(),
diff --git a/core/src/memory.rs b/core/src/memory.rs
index dad32ac19..670cc409e 100644
--- a/core/src/memory.rs
+++ b/core/src/memory.rs
@@ -141,20 +141,20 @@ impl Memory {
 		len: U256,
 		data: &[u8],
 	) -> Result<(), ExitFatal> {
-		let memory_offset = if memory_offset > U256::from(usize::MAX) {
+		let memory_offset = if memory_offset > crate::utils::U256_USIZE_MAX {
 			return Err(ExitFatal::NotSupported);
 		} else {
 			memory_offset.as_usize()
 		};
 
-		let ulen = if len > U256::from(usize::MAX) {
+		let ulen = if len > crate::utils::U256_USIZE_MAX {
 			return Err(ExitFatal::NotSupported);
 		} else {
 			len.as_usize()
 		};
 
 		let data = if let Some(end) = data_offset.checked_add(len) {
-			if end > U256::from(usize::MAX) {
+			if end > crate::utils::U256_USIZE_MAX {
 				&[]
 			} else {
 				let data_offset = data_offset.as_usize();
diff --git a/core/src/utils.rs b/core/src/utils.rs
index c78dd49e6..b3f639e8e 100644
--- a/core/src/utils.rs
+++ b/core/src/utils.rs
@@ -2,6 +2,13 @@ use core::cmp::Ordering;
 use core::ops::{Div, Rem};
 use primitive_types::U256;
 
+pub const U256_USIZE_MAX: U256 = {
+	// TODO: assert!(core::mem::size_of::<usize>() <= core::mem::size_of::<u64>());
+	let mut ret = [0; 4];
+	ret[0] = usize::MAX as u64;
+	U256(ret)
+};
+
 #[derive(Copy, Clone, Eq, PartialEq, Debug)]
 pub enum Sign {
 	Plus,