Separate unsigned and signed safemath libraries

CHANGELOG.md

@@ -11,7 +11,7 @@
  * `ERC721`: added `_burn(uint256 tokenId)`, replacing the similar deprecated function (see below). ([#1550](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1550))
  * `ERC721`: added `_tokensOfOwner(address owner)`, allowing to internally retrieve the array of an account's owned tokens. ([#1522](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1522))
  * Crowdsales: all constructors are now `public`, meaning it is not necessary to extend these contracts in order to deploy them. The exception is `FinalizableCrowdsale`, since it is meaningless unless extended. ([#1564](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1564))
- * `SafeMath`: added overflow-safe operations for signed integers (`int256`). ([#1559](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1559))
+ * `SignedSafeMath`: added overflow-safe operations for signed integers (`int256`). ([#1559](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1559), [#1588](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1588))
 
 ### Improvements:
  * The compiler version required by `Array` was behind the rest of the libray so it was updated to `v0.4.24`. ([#1553](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1553))

contracts/drafts/SignedSafeMath.sol

@@ -0,0 +1,60 @@
+pragma solidity ^0.5.0;
+
+/**
+ * @title SignedSafeMath
+ * @dev Signed math operations with safety checks that revert on error
+ */
+library SignedSafeMath {
+    int256 constant private INT256_MIN = -2**255;
+
+    /**
+    * @dev Multiplies two signed integers, reverts on overflow.
+    */
+    function mul(int256 a, int256 b) internal pure returns (int256) {
+        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
+        // benefit is lost if 'b' is also tested.
+        // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
+        if (a == 0) {
+            return 0;
+        }
+
+        require(!(a == -1 && b == INT256_MIN)); // This is the only case of overflow not detected by the check below
+
+        int256 c = a * b;
+        require(c / a == b);
+
+        return c;
+    }
+
+    /**
+    * @dev Integer division of two signed integers truncating the quotient, reverts on division by zero.
+    */
+    function div(int256 a, int256 b) internal pure returns (int256) {
+        require(b != 0); // Solidity only automatically asserts when dividing by 0
+        require(!(b == -1 && a == INT256_MIN)); // This is the only case of overflow
+
+        int256 c = a / b;
+
+        return c;
+    }
+
+    /**
+    * @dev Subtracts two signed integers, reverts on overflow.
+    */
+    function sub(int256 a, int256 b) internal pure returns (int256) {
+        int256 c = a - b;
+        require((b >= 0 && c <= a) || (b < 0 && c > a));
+
+        return c;
+    }
+
+    /**
+    * @dev Adds two signed integers, reverts on overflow.
+    */
+    function add(int256 a, int256 b) internal pure returns (int256) {
+        int256 c = a + b;
+        require((b >= 0 && c >= a) || (b < 0 && c < a));
+
+        return c;
+    }
+}

contracts/math/SafeMath.sol

@@ -2,11 +2,9 @@ pragma solidity ^0.5.0;
 
 /**
  * @title SafeMath
- * @dev Math operations with safety checks that revert on error
+ * @dev Unsigned math operations with safety checks that revert on error
  */
 library SafeMath {
-    int256 constant private INT256_MIN = -2**255;
-
     /**
     * @dev Multiplies two unsigned integers, reverts on overflow.
     */
@@ -24,25 +22,6 @@ library SafeMath {
         return c;
     }
 
-    /**
-    * @dev Multiplies two signed integers, reverts on overflow.
-    */
-    function mul(int256 a, int256 b) internal pure returns (int256) {
-        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
-        // benefit is lost if 'b' is also tested.
-        // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
-        if (a == 0) {
-            return 0;
-        }
-
-        require(!(a == -1 && b == INT256_MIN)); // This is the only case of overflow not detected by the check below
-
-        int256 c = a * b;
-        require(c / a == b);
-
-        return c;
-    }
-
     /**
     * @dev Integer division of two unsigned integers truncating the quotient, reverts on division by zero.
     */
@@ -55,18 +34,6 @@ library SafeMath {
         return c;
     }
 
-    /**
-    * @dev Integer division of two signed integers truncating the quotient, reverts on division by zero.
-    */
-    function div(int256 a, int256 b) internal pure returns (int256) {
-        require(b != 0); // Solidity only automatically asserts when dividing by 0
-        require(!(b == -1 && a == INT256_MIN)); // This is the only case of overflow
-
-        int256 c = a / b;
-
-        return c;
-    }
-
     /**
     * @dev Subtracts two unsigned integers, reverts on overflow (i.e. if subtrahend is greater than minuend).
     */
@@ -77,16 +44,6 @@ library SafeMath {
         return c;
     }
 
-    /**
-    * @dev Subtracts two signed integers, reverts on overflow.
-    */
-    function sub(int256 a, int256 b) internal pure returns (int256) {
-        int256 c = a - b;
-        require((b >= 0 && c <= a) || (b < 0 && c > a));
-
-        return c;
-    }
-
     /**
     * @dev Adds two unsigned integers, reverts on overflow.
     */
@@ -97,16 +54,6 @@ library SafeMath {
         return c;
     }
 
-    /**
-    * @dev Adds two signed integers, reverts on overflow.
-    */
-    function add(int256 a, int256 b) internal pure returns (int256) {
-        int256 c = a + b;
-        require((b >= 0 && c >= a) || (b < 0 && c < a));
-
-        return c;
-    }
-
     /**
     * @dev Divides two unsigned integers and returns the remainder (unsigned integer modulo),
     * reverts when dividing by zero.

contracts/mocks/SafeMathMock.sol

@@ -1,43 +1,25 @@
 pragma solidity ^0.5.0;
 
-
 import "../math/SafeMath.sol";
 
-
 contract SafeMathMock {
-    function mulUints(uint256 a, uint256 b) public pure returns (uint256) {
+    function mul(uint256 a, uint256 b) public pure returns (uint256) {
         return SafeMath.mul(a, b);
     }
 
-    function mulInts(int256 a, int256 b) public pure returns (int256) {
-        return SafeMath.mul(a, b);
-    }
-
-    function divUints(uint256 a, uint256 b) public pure returns (uint256) {
-        return SafeMath.div(a, b);
-    }
-
-    function divInts(int256 a, int256 b) public pure returns (int256) {
+    function div(uint256 a, uint256 b) public pure returns (uint256) {
         return SafeMath.div(a, b);
     }
 
-    function subUints(uint256 a, uint256 b) public pure returns (uint256) {
-        return SafeMath.sub(a, b);
-    }
-
-    function subInts(int256 a, int256 b) public pure returns (int256) {
+    function sub(uint256 a, uint256 b) public pure returns (uint256) {
         return SafeMath.sub(a, b);
     }
 
-    function addUints(uint256 a, uint256 b) public pure returns (uint256) {
-        return SafeMath.add(a, b);
-    }
-
-    function addInts(int256 a, int256 b) public pure returns (int256) {
+    function add(uint256 a, uint256 b) public pure returns (uint256) {
         return SafeMath.add(a, b);
     }
 
-    function modUints(uint256 a, uint256 b) public pure returns (uint256) {
+    function mod(uint256 a, uint256 b) public pure returns (uint256) {
         return SafeMath.mod(a, b);
     }
 }

contracts/mocks/SignedSafeMathMock.sol

@@ -0,0 +1,21 @@
+pragma solidity ^0.5.0;
+
+import "../drafts/SignedSafeMath.sol";
+
+contract SignedSafeMathMock {
+    function mul(int256 a, int256 b) public pure returns (int256) {
+        return SignedSafeMath.mul(a, b);
+    }
+
+    function div(int256 a, int256 b) public pure returns (int256) {
+        return SignedSafeMath.div(a, b);
+    }
+
+    function sub(int256 a, int256 b) public pure returns (int256) {
+        return SignedSafeMath.sub(a, b);
+    }
+
+    function add(int256 a, int256 b) public pure returns (int256) {
+        return SignedSafeMath.add(a, b);
+    }
+}

test/drafts/SignedSafeMath.test.js

@@ -0,0 +1,138 @@
+const shouldFail = require('../helpers/shouldFail');
+const { MIN_INT256, MAX_INT256 } = require('../helpers/constants');
+
+const SignedSafeMathMock = artifacts.require('SignedSafeMathMock');
+
+const { BigNumber } = require('../helpers/setup');
+
+contract('SignedSafeMath', function () {
+  beforeEach(async function () {
+    this.safeMath = await SignedSafeMathMock.new();
+  });
+
+  describe('add', function () {
+    it('adds correctly if it does not overflow and the result is positve', async function () {
+      const a = new BigNumber(1234);
+      const b = new BigNumber(5678);
+
+      (await this.safeMath.add(a, b)).should.be.bignumber.equal(a.plus(b));
+    });
+
+    it('adds correctly if it does not overflow and the result is negative', async function () {
+      const a = MAX_INT256;
+      const b = MIN_INT256;
+
+      const result = await this.safeMath.add(a, b);
+      result.should.be.bignumber.equal(a.plus(b));
+    });
+
+    it('reverts on positive addition overflow', async function () {
+      const a = MAX_INT256;
+      const b = new BigNumber(1);
+
+      await shouldFail.reverting(this.safeMath.add(a, b));
+    });
+
+    it('reverts on negative addition overflow', async function () {
+      const a = MIN_INT256;
+      const b = new BigNumber(-1);
+
+      await shouldFail.reverting(this.safeMath.add(a, b));
+    });
+  });
+
+  describe('sub', function () {
+    it('subtracts correctly if it does not overflow and the result is positive', async function () {
+      const a = new BigNumber(5678);
+      const b = new BigNumber(1234);
+
+      const result = await this.safeMath.sub(a, b);
+      result.should.be.bignumber.equal(a.minus(b));
+    });
+
+    it('subtracts correctly if it does not overflow and the result is negative', async function () {
+      const a = new BigNumber(1234);
+      const b = new BigNumber(5678);
+
+      const result = await this.safeMath.sub(a, b);
+      result.should.be.bignumber.equal(a.minus(b));
+    });
+
+    it('reverts on positive subtraction overflow', async function () {
+      const a = MAX_INT256;
+      const b = new BigNumber(-1);
+
+      await shouldFail.reverting(this.safeMath.sub(a, b));
+    });
+
+    it('reverts on negative subtraction overflow', async function () {
+      const a = MIN_INT256;
+      const b = new BigNumber(1);
+
+      await shouldFail.reverting(this.safeMath.sub(a, b));
+    });
+  });
+
+  describe('mul', function () {
+    it('multiplies correctly', async function () {
+      const a = new BigNumber(5678);
+      const b = new BigNumber(-1234);
+
+      const result = await this.safeMath.mul(a, b);
+      result.should.be.bignumber.equal(a.times(b));
+    });
+
+    it('handles a zero product correctly', async function () {
+      const a = new BigNumber(0);
+      const b = new BigNumber(5678);
+
+      const result = await this.safeMath.mul(a, b);
+      result.should.be.bignumber.equal(a.times(b));
+    });
+
+    it('reverts on multiplication overflow, positive operands', async function () {
+      const a = MAX_INT256;
+      const b = new BigNumber(2);
+
+      await shouldFail.reverting(this.safeMath.mul(a, b));
+    });
+
+    it('reverts when minimum integer is multiplied by -1', async function () {
+      const a = MIN_INT256;
+      const b = new BigNumber(-1);
+
+      await shouldFail.reverting(this.safeMath.mul(a, b));
+    });
+
+    it('reverts when -1 is multiplied by minimum integer', async function () {
+      const a = new BigNumber(-1);
+      const b = MIN_INT256;
+
+      await shouldFail.reverting(this.safeMath.mul(a, b));
+    });
+  });
+
+  describe('div', function () {
+    it('divides correctly', async function () {
+      const a = new BigNumber(-5678);
+      const b = new BigNumber(5678);
+
+      const result = await this.safeMath.div(a, b);
+      result.should.be.bignumber.equal(a.div(b));
+    });
+
+    it('reverts on zero division', async function () {
+      const a = new BigNumber(-5678);
+      const b = new BigNumber(0);
+
+      await shouldFail.reverting(this.safeMath.div(a, b));
+    });
+
+    it('reverts on overflow, negative second', async function () {
+      const a = new BigNumber(MIN_INT256);
+      const b = new BigNumber(-1);
+
+      await shouldFail.reverting(this.safeMath.div(a, b));
+    });
+  });
+});