From 2e8ca596a8055f39e7f37343498845c622d5adc4 Mon Sep 17 00:00:00 2001
From: Jay Paik <jaypaik@users.noreply.github.com>
Date: Tue, 15 Oct 2024 14:33:20 -0400
Subject: [PATCH] feat: SparseCalldataSegmentLib optimization (#200)

---
 src/helpers/EmptyCalldataSlice.sol         | 12 ++++++++++++
 src/libraries/SparseCalldataSegmentLib.sol |  5 +++--
 2 files changed, 15 insertions(+), 2 deletions(-)
 create mode 100644 src/helpers/EmptyCalldataSlice.sol

diff --git a/src/helpers/EmptyCalldataSlice.sol b/src/helpers/EmptyCalldataSlice.sol
new file mode 100644
index 00000000..381f5765
--- /dev/null
+++ b/src/helpers/EmptyCalldataSlice.sol
@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: GPL-3.0
+pragma solidity ^0.8.20;
+
+function getEmptyCalldataSlice() pure returns (bytes calldata) {
+    bytes calldata empty;
+
+    assembly ("memory-safe") {
+        empty.length := 0
+    }
+
+    return empty;
+}
diff --git a/src/libraries/SparseCalldataSegmentLib.sol b/src/libraries/SparseCalldataSegmentLib.sol
index 17f1e680..5b27c6ae 100644
--- a/src/libraries/SparseCalldataSegmentLib.sol
+++ b/src/libraries/SparseCalldataSegmentLib.sol
@@ -2,6 +2,7 @@
 pragma solidity ^0.8.20;
 
 import {RESERVED_VALIDATION_DATA_INDEX} from "../helpers/Constants.sol";
+import {getEmptyCalldataSlice} from "../helpers/EmptyCalldataSlice.sol";
 
 /// @title Sparse Calldata Segment Library
 /// @notice Library for working with sparsely-packed calldata segments, identified with an index.
@@ -51,7 +52,7 @@ library SparseCalldataSegmentLib {
     function advanceSegmentIfAtIndex(bytes calldata source, uint8 index)
         internal
         pure
-        returns (bytes memory, bytes calldata)
+        returns (bytes calldata, bytes calldata)
     {
         uint8 nextIndex = getIndex(source);
 
@@ -69,7 +70,7 @@ library SparseCalldataSegmentLib {
             return (segment, remainder);
         }
 
-        return ("", source);
+        return (getEmptyCalldataSlice(), source);
     }
 
     /// @notice Extracts the final segment from the source.