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Vectorized · Jan 17, 2025 · 1a49dc3 · 1a49dc3
1 parent 51a5a7e
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Showing 2 changed files with 28 additions and 12 deletions.
diff --git a/src/utils/LibBit.sol b/src/utils/LibBit.sol
@@ -117,14 +117,25 @@ library LibBit {
         }
     }
 
-    /// @dev Returns the common prefix of `x` and `y` in hex format.
-    function commonPrefix(uint256 x, uint256 y) internal pure returns (uint256 r) {
-        uint256 lz = clz(x ^ y);
-        assembly {
-            let nibbles := div(lz, 4)
-            // Since nibbles is always <= 64, there's no risk of underflow.
-            let bits := mul(sub(64, nibbles), 4)
-            r := shl(bits, shr(bits, x))
+    /// @dev Returns the common prefix of `x` and `y` at the bit level.
+    function commonBitPrefix(uint256 x, uint256 y) internal pure returns (uint256 r) {
+        r = clz(x ^ y);
+        r = (x >> r) << r;
+    }
+
+    /// @dev Returns the common prefix of `x` and `y` at the nibble level.
+    function commonNibblePrefix(uint256 x, uint256 y) internal pure returns (uint256 r) {
+        unchecked {
+            uint256 s = (64 - (clz(x ^ y) >> 2)) << 2;
+            r = (x >> s) << s;
+        }
+    }
+
+    /// @dev Returns the common prefix of `x` and `y` at the byte level.
+    function commonBytePrefix(uint256 x, uint256 y) internal pure returns (uint256 r) {
+        unchecked {
+            uint256 s = (32 - (clz(x ^ y) >> 3)) << 3;
+            r = (x >> s) << s;
         }
     }
 

diff --git a/test/LibBit.t.sol b/test/LibBit.t.sol
@@ -226,15 +226,20 @@ contract LibBitTest is SoladyTest {
     }
 
     function testCommonPrefix() public {
-        assertEq(LibBit.commonPrefix(0x1, 0x2), 0);
-        assertEq(LibBit.commonPrefix(0x1234abc, 0x1234bbb), 0x1234000);
-        assertEq(LibBit.commonPrefix(0x1234abc, 0x1234abc), 0x1234abc);
+        assertEq(LibBit.commonNibblePrefix(0x1, 0x2), 0);
+        assertEq(LibBit.commonNibblePrefix(0x1234abc, 0x1234bbb), 0x1234000);
+        assertEq(LibBit.commonNibblePrefix(0x1234abc, 0x1234abc), 0x1234abc);
+
+        assertEq(LibBit.commonBytePrefix(0xaabbcc, 0xaabbcc), 0xaabbcc);
+        assertEq(LibBit.commonBytePrefix(0xaabbcc, 0xaabbc0), 0xaabb00);
+        assertEq(LibBit.commonBytePrefix(0xaabbcc, 0xaab0c0), 0xaa0000);
+        assertEq(LibBit.commonBytePrefix(0xaabbcc, 0xa0b0c0), 0x000000);
     }
 
     function testCommonPrefix(uint256 x, uint8 p) public {
         uint256 y = x ^ (1 << p);
         uint256 l = 63 - p / 4;
         uint256 r = l == 0 ? 0 : x & ~((1 << ((64 - l) * 4)) - 1);
-        assertEq(LibBit.commonPrefix(x, y), r);
+        assertEq(LibBit.commonNibblePrefix(x, y), r);
     }
 }