Adding SafeCast variants for signed integers (#2243)

* feat: Adding SafeCast variants for signed integers

* Add newline at EOF

* Update CHANGELOG.md

* Update contracts/utils/SafeCast.sol

Co-authored-by: Nicolás Venturo <nicolas.venturo@gmail.com>

Co-authored-by: Nicolás Venturo <nicolas.venturo@gmail.com>

contracts/utils/SafeCast.sol

@@ -4,10 +4,10 @@ pragma solidity ^0.6.0;
 
 
 /**
- * @dev Wrappers over Solidity's uintXX casting operators with added overflow
+ * @dev Wrappers over Solidity's uintXX/intXX casting operators with added overflow
  * checks.
  *
- * Downcasting from uint256 in Solidity does not revert on overflow. This can
+ * Downcasting from uint256/int256 in Solidity does not revert on overflow. This can
  * easily result in undesired exploitation or bugs, since developers usually
  * assume that overflows raise errors. `SafeCast` restores this intuition by
  * reverting the transaction when such an operation overflows.
@@ -15,8 +15,8 @@ pragma solidity ^0.6.0;
  * Using this library instead of the unchecked operations eliminates an entire
  * class of bugs, so it's recommended to use it always.
  *
- * Can be combined with {SafeMath} to extend it to smaller types, by performing
- * all math on `uint256` and then downcasting.
+ * Can be combined with {SafeMath} and {SignedSafeMath} to extend it to smaller types, by performing
+ * all math on `uint256` and `int256` and then downcasting.
  */
 library SafeCast {
 
@@ -107,6 +107,86 @@ library SafeCast {
         return uint256(value);
     }
 
+    /**
+     * @dev Returns the downcasted int128 from int256, reverting on
+     * overflow (when the input is less than smallest int128 or
+     * greater than largest int128).
+     *
+     * Counterpart to Solidity's `int128` operator.
+     *
+     * Requirements:
+     *
+     * - input must fit into 128 bits
+     */
+    function toInt128(int256 value) internal pure returns (int128) {
+        require(value >= -2**127 && value < 2**127, "SafeCast: value doesn\'t fit in 128 bits");
+        return int128(value);
+    }
+
+    /**
+     * @dev Returns the downcasted int64 from int256, reverting on
+     * overflow (when the input is less than smallest int64 or
+     * greater than largest int64).
+     *
+     * Counterpart to Solidity's `int64` operator.
+     *
+     * Requirements:
+     *
+     * - input must fit into 64 bits
+     */
+    function toInt64(int256 value) internal pure returns (int64) {
+        require(value >= -2**63 && value < 2**63, "SafeCast: value doesn\'t fit in 64 bits");
+        return int64(value);
+    }
+
+    /**
+     * @dev Returns the downcasted int32 from int256, reverting on
+     * overflow (when the input is less than smallest int32 or
+     * greater than largest int32).
+     *
+     * Counterpart to Solidity's `int32` operator.
+     *
+     * Requirements:
+     *
+     * - input must fit into 32 bits
+     */
+    function toInt32(int256 value) internal pure returns (int32) {
+        require(value >= -2**31 && value < 2**31, "SafeCast: value doesn\'t fit in 32 bits");
+        return int32(value);
+    }
+
+    /**
+     * @dev Returns the downcasted int16 from int256, reverting on
+     * overflow (when the input is less than smallest int16 or
+     * greater than largest int16).
+     *
+     * Counterpart to Solidity's `int16` operator.
+     *
+     * Requirements:
+     *
+     * - input must fit into 16 bits
+     */
+    function toInt16(int256 value) internal pure returns (int16) {
+        require(value >= -2**15 && value < 2**15, "SafeCast: value doesn\'t fit in 16 bits");
+        return int16(value);
+    }
+
+    /**
+     * @dev Returns the downcasted int8 from int256, reverting on
+     * overflow (when the input is less than smallest int8 or
+     * greater than largest int8).
+     *
+     * Counterpart to Solidity's `int8` operator.
+     *
+     * Requirements:
+     *
+     * - input must fit into 8 bits.
+     */
+    function toInt8(int256 value) internal pure returns (int8) {
+        require(value >= -2**7 && value < 2**7, "SafeCast: value doesn\'t fit in 8 bits");
+        return int8(value);
+    }
+
     /**
      * @dev Converts an unsigned uint256 into a signed int256.
      *