From 1b3b258ccc89d580f7caddf5d809dc21c3bc826c Mon Sep 17 00:00:00 2001
From: Mark Spanbroek <mark@spanbroek.net>
Date: Mon, 22 Jan 2024 15:38:25 +0100
Subject: [PATCH] Conversion between little and big endian

---
 contracts/Endian.sol     | 14 ++++++++++++++
 contracts/TestEndian.sol | 10 ++++++++++
 test/Endian.test.js      | 22 ++++++++++++++++++++++
 3 files changed, 46 insertions(+)
 create mode 100644 contracts/Endian.sol
 create mode 100644 contracts/TestEndian.sol
 create mode 100644 test/Endian.test.js

diff --git a/contracts/Endian.sol b/contracts/Endian.sol
new file mode 100644
index 0000000..68fc971
--- /dev/null
+++ b/contracts/Endian.sol
@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.8;
+
+contract Endian {
+  /// reverses byte order to allow conversion between little endian and big
+  /// endian integers
+  function _byteSwap(bytes32 input) internal pure returns (bytes32 output) {
+    output = output | bytes1(input);
+    for (uint i = 1; i < 32; i++) {
+      output = output >> 8;
+      output = output | bytes1(input << (i * 8));
+    }
+  }
+}
diff --git a/contracts/TestEndian.sol b/contracts/TestEndian.sol
new file mode 100644
index 0000000..7ee7df9
--- /dev/null
+++ b/contracts/TestEndian.sol
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+import "./Endian.sol";
+
+contract TestEndian is Endian {
+  function byteSwap(bytes32 input) public pure returns (bytes32) {
+    return _byteSwap(input);
+  }
+}
diff --git a/test/Endian.test.js b/test/Endian.test.js
new file mode 100644
index 0000000..1380323
--- /dev/null
+++ b/test/Endian.test.js
@@ -0,0 +1,22 @@
+const { expect } = require("chai")
+const { ethers } = require("hardhat")
+
+describe("Endian", function () {
+  const big = "0x000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f"
+  const little = "0x1f1e1d1c1b1a191817161514131211100f0e0d0c0b0a09080706050403020100"
+
+  let endian
+
+  beforeEach(async function () {
+    let Endian = await ethers.getContractFactory("TestEndian")
+    endian = await Endian.deploy()
+  })
+
+  it("converts from little endian to big endian", async function () {
+    expect(await endian.byteSwap(little)).to.equal(big)
+  })
+
+  it("converts from big endian to little endian", async function () {
+    expect(await endian.byteSwap(big)).to.equal(little)
+  })
+})