From 51a5a7ee879ea2ddc7fe69164bd6f008716bbb33 Mon Sep 17 00:00:00 2001
From: JChoy <jchoyeclipse@gmail.com>
Date: Fri, 17 Jan 2025 08:17:52 +0900
Subject: [PATCH] =?UTF-8?q?=E2=9C=A8=20Add=20commonPrefix=20(#1306)?=
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---
src/utils/LibBit.sol | 11 +++++++++++
test/LibBit.t.sol | 13 +++++++++++++
2 files changed, 24 insertions(+)
diff --git a/src/utils/LibBit.sol b/src/utils/LibBit.sol
index eb617691a0..b6a8826cd1 100644
--- a/src/utils/LibBit.sol
+++ b/src/utils/LibBit.sol
@@ -117,6 +117,17 @@ 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))
+ }
+ }
+
/*´:°•.°+.*•´.*:˚.°*.˚•´.°:°•.°•.*•´.*:˚.°*.˚•´.°:°•.°+.*•´.*:*/
/* BOOLEAN OPERATIONS */
/*.•°:°.´+˚.*°.˚:*.´•*.+°.•°:´*.´•*.•°.•°:°.´:•˚°.*°.˚:*.´+°.•*/
diff --git a/test/LibBit.t.sol b/test/LibBit.t.sol
index 2d9694288c..ba641b1b53 100644
--- a/test/LibBit.t.sol
+++ b/test/LibBit.t.sol
@@ -224,4 +224,17 @@ contract LibBitTest is SoladyTest {
r := mload(0x00)
}
}
+
+ function testCommonPrefix() public {
+ assertEq(LibBit.commonPrefix(0x1, 0x2), 0);
+ assertEq(LibBit.commonPrefix(0x1234abc, 0x1234bbb), 0x1234000);
+ assertEq(LibBit.commonPrefix(0x1234abc, 0x1234abc), 0x1234abc);
+ }
+
+ 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);
+ }
}