From f6db5c1f309e44a057f20ef83b76fc81ddd7e21b Mon Sep 17 00:00:00 2001
From: barakman <barakman@yahoo.com>
Date: Wed, 24 Nov 2021 14:09:05 +0100
Subject: [PATCH] A function which returns the absolute value of a signed value
 (#2984)

* Add a function which returns the absolute (and obviously unsigned) value of a signed value.

* add changelog entry and fix lint

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>
---
 CHANGELOG.md                  |  1 +
 contracts/mocks/MathMock.sol  |  4 ++++
 contracts/utils/math/Math.sol | 10 ++++++++++
 test/utils/math/Math.test.js  | 18 +++++++++++++++++-
 4 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a6a8d4e0f..009a2fa4c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 ## Unreleased
 
 * `GovernorTimelockControl`: improve the `state()` function to have it reflect cases where a proposal has been canceled directly on the timelock. ([#2977](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2977))
+* `Math`: add a `abs(int256)` method that returns the unsigned absolute value of a signed value. ([#2984](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2984))
 
 ## Unreleased
 
diff --git a/contracts/mocks/MathMock.sol b/contracts/mocks/MathMock.sol
index c651b6bb1..f6c11acb4 100644
--- a/contracts/mocks/MathMock.sol
+++ b/contracts/mocks/MathMock.sol
@@ -20,4 +20,8 @@ contract MathMock {
     function ceilDiv(uint256 a, uint256 b) public pure returns (uint256) {
         return Math.ceilDiv(a, b);
     }
+
+    function abs(int256 n) public pure returns (uint256) {
+        return Math.abs(n);
+    }
 }
diff --git a/contracts/utils/math/Math.sol b/contracts/utils/math/Math.sol
index b31bca303..52944c2ee 100644
--- a/contracts/utils/math/Math.sol
+++ b/contracts/utils/math/Math.sol
@@ -40,4 +40,14 @@ library Math {
         // (a + b - 1) / b can overflow on addition, so we distribute.
         return a / b + (a % b == 0 ? 0 : 1);
     }
+
+    /**
+     * @dev Returns the absolute unsigned value of a signed value.
+     */
+    function abs(int256 n) internal pure returns (uint256) {
+        unchecked {
+            // must be unchecked in order to support `n = type(int256).min`
+            return uint256(n >= 0 ? n : -n);
+        }
+    }
 }
diff --git a/test/utils/math/Math.test.js b/test/utils/math/Math.test.js
index 7e194dec7..eff64b720 100644
--- a/test/utils/math/Math.test.js
+++ b/test/utils/math/Math.test.js
@@ -1,6 +1,6 @@
 const { BN, constants } = require('@openzeppelin/test-helpers');
 const { expect } = require('chai');
-const { MAX_UINT256 } = constants;
+const { MAX_UINT256, MAX_INT256, MIN_INT256 } = constants;
 
 const MathMock = artifacts.require('MathMock');
 
@@ -85,4 +85,20 @@ contract('Math', function (accounts) {
       expect(await this.math.ceilDiv(MAX_UINT256, b)).to.be.bignumber.equal(MAX_UINT256);
     });
   });
+
+  describe('abs', function () {
+    for (const n of [
+      MIN_INT256,
+      MIN_INT256.addn(1),
+      new BN('-1'),
+      new BN('0'),
+      new BN('1'),
+      MAX_INT256.subn(1),
+      MAX_INT256,
+    ]) {
+      it(`correctly computes the absolute value of ${n}`, async function () {
+        expect(await this.math.abs(n)).to.be.bignumber.equal(n.abs());
+      });
+    }
+  });
 });