Adds safeCastTo16

Author: robertabbott

.gas-snapshot

@@ -176,23 +176,25 @@ SSTORE2Test:testWriteReadEmptyBound() (gas: 34677)
 SSTORE2Test:testWriteReadFullBoundedRead() (gas: 53672)
 SSTORE2Test:testWriteReadFullStartBound() (gas: 34764)
 SafeCastLibTest:testFailSafeCastTo128() (gas: 321)
+SafeCastLibTest:testFailSafeCastTo16() (gas: 343)
 SafeCastLibTest:testFailSafeCastTo160() (gas: 342)
 SafeCastLibTest:testFailSafeCastTo192() (gas: 322)
-SafeCastLibTest:testFailSafeCastTo224() (gas: 343)
-SafeCastLibTest:testFailSafeCastTo248() (gas: 365)
+SafeCastLibTest:testFailSafeCastTo224() (gas: 365)
+SafeCastLibTest:testFailSafeCastTo248() (gas: 321)
 SafeCastLibTest:testFailSafeCastTo32() (gas: 364)
-SafeCastLibTest:testFailSafeCastTo64() (gas: 321)
+SafeCastLibTest:testFailSafeCastTo64() (gas: 343)
 SafeCastLibTest:testFailSafeCastTo8() (gas: 341)
-SafeCastLibTest:testFailSafeCastTo96() (gas: 321)
+SafeCastLibTest:testFailSafeCastTo96() (gas: 343)
 SafeCastLibTest:testSafeCastTo128() (gas: 472)
+SafeCastLibTest:testSafeCastTo16() (gas: 447)
 SafeCastLibTest:testSafeCastTo160() (gas: 470)
 SafeCastLibTest:testSafeCastTo192() (gas: 449)
 SafeCastLibTest:testSafeCastTo224() (gas: 491)
-SafeCastLibTest:testSafeCastTo24() (gas: 470)
+SafeCastLibTest:testSafeCastTo24() (gas: 492)
 SafeCastLibTest:testSafeCastTo248() (gas: 450)
 SafeCastLibTest:testSafeCastTo32() (gas: 449)
-SafeCastLibTest:testSafeCastTo64() (gas: 470)
-SafeCastLibTest:testSafeCastTo8() (gas: 469)
+SafeCastLibTest:testSafeCastTo64() (gas: 492)
+SafeCastLibTest:testSafeCastTo8() (gas: 491)
 SafeCastLibTest:testSafeCastTo96() (gas: 469)
 SafeTransferLibTest:testApproveWithMissingReturn() (gas: 30751)
 SafeTransferLibTest:testApproveWithNonContract() (gas: 3035)

src/test/SafeCastLib.t.sol

@@ -51,6 +51,11 @@ contract SafeCastLibTest is DSTestPlus {
         assertEq(SafeCastLib.safeCastTo24(2.5e3), 2.5e3);
     }
 
+    function testSafeCastTo16() public {
+        assertEq(SafeCastLib.safeCastTo16(2.5e3), 2.5e3);
+        assertEq(SafeCastLib.safeCastTo16(2.5e2), 2.5e2);
+    }
+
     function testSafeCastTo8() public {
         assertEq(SafeCastLib.safeCastTo8(100), 100);
         assertEq(SafeCastLib.safeCastTo8(250), 250);
@@ -88,6 +93,10 @@ contract SafeCastLibTest is DSTestPlus {
         SafeCastLib.safeCastTo32(type(uint32).max + 1);
     }
 
+    function testFailSafeCastTo16() public pure {
+        SafeCastLib.safeCastTo16(type(uint16).max + 1);
+    }
+
     function testFailSafeCastTo8() public pure {
         SafeCastLib.safeCastTo8(type(uint8).max + 1);
     }
@@ -140,6 +149,12 @@ contract SafeCastLibTest is DSTestPlus {
         assertEq(SafeCastLib.safeCastTo32(x), x);
     }
 
+    function testSafeCastTo16(uint256 x) public {
+        x = bound(x, 0, type(uint16).max);
+
+        assertEq(SafeCastLib.safeCastTo16(x), x);
+    }
+
     function testSafeCastTo8(uint256 x) public {
         x = bound(x, 0, type(uint8).max);
 
@@ -200,6 +215,12 @@ contract SafeCastLibTest is DSTestPlus {
         SafeCastLib.safeCastTo24(x);
     }
 
+    function testFailSafeCastTo16(uint256 x) public {
+        x = bound(x, type(uint16).max + 1, type(uint256).max);
+
+        SafeCastLib.safeCastTo16(x);
+    }
+
     function testFailSafeCastTo8(uint256 x) public {
         x = bound(x, type(uint8).max + 1, type(uint256).max);
 

src/utils/SafeCastLib.sol

@@ -59,6 +59,12 @@ library SafeCastLib {
         y = uint24(x);
     }
 
+    function safeCastTo16(uint256 x) internal pure returns (uint16 y) {
+        require(x < 1 << 16);
+
+        y = uint16(x);
+    }
+
     function safeCastTo8(uint256 x) internal pure returns (uint8 y) {
         require(x < 1 << 8);