From e5fb718d4071b4be5e8dc980a3733616605c570a Mon Sep 17 00:00:00 2001
From: carter-ya <liukefeng2008@hotmail.com>
Date: Thu, 23 Nov 2023 23:31:14 +0800
Subject: [PATCH] Optimized gas costs in `ceilDiv` (#4553)

---
 .changeset/angry-dodos-grow.md |  5 +++++
 contracts/utils/math/Math.sol  | 10 ++++++++--
 test/utils/math/Math.t.sol     |  9 +++++----
 3 files changed, 18 insertions(+), 6 deletions(-)
 create mode 100644 .changeset/angry-dodos-grow.md

diff --git a/.changeset/angry-dodos-grow.md b/.changeset/angry-dodos-grow.md
new file mode 100644
index 000000000..ab2b60104
--- /dev/null
+++ b/.changeset/angry-dodos-grow.md
@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`Math`: Optimized gas cost of `ceilDiv` by using `unchecked`.
diff --git a/contracts/utils/math/Math.sol b/contracts/utils/math/Math.sol
index 968152452..86316cb29 100644
--- a/contracts/utils/math/Math.sol
+++ b/contracts/utils/math/Math.sol
@@ -110,8 +110,14 @@ library Math {
             return a / b;
         }
 
-        // (a + b - 1) / b can overflow on addition, so we distribute.
-        return a == 0 ? 0 : (a - 1) / b + 1;
+        // The following calculation ensures accurate ceiling division without overflow.
+        // Since a is non-zero, (a - 1) / b will not overflow.
+        // The largest possible result occurs when (a - 1) / b is type(uint256).max,
+        // but the largest value we can obtain is type(uint256).max - 1, which happens
+        // when a = type(uint256).max and b = 1.
+        unchecked {
+            return a == 0 ? 0 : (a - 1) / b + 1;
+        }
     }
 
     /**
diff --git a/test/utils/math/Math.t.sol b/test/utils/math/Math.t.sol
index 0b497a858..a75783379 100644
--- a/test/utils/math/Math.t.sol
+++ b/test/utils/math/Math.t.sol
@@ -16,10 +16,11 @@ contract MathTest is Test {
         if (result == 0) {
             assertEq(a, 0);
         } else {
-            uint256 maxdiv = UINT256_MAX / b;
-            bool overflow = maxdiv * b < a;
-            assertTrue(a > b * (result - 1));
-            assertTrue(overflow ? result == maxdiv + 1 : a <= b * result);
+            uint256 expect = a / b;
+            if (expect * b < a) {
+                expect += 1;
+            }
+            assertEq(result, expect);
         }
     }