adds parseBTCTaprootAddress

src/BTCDepositAddressDeriver.sol

@@ -2,6 +2,16 @@
 
 pragma solidity ^0.8.24;
 
+import {Deriver} from "./Deriver.sol";
+import {Bech32m} from "./Bech32m.sol";
+
+error UnsupportedBtcAddress(string btcAddress);
+error CannotParseBtcAddress(
+    string btcAddress,
+    string hrp,
+    Bech32m.DecodeError err
+);
+
 contract BTCDepositAddressDeriver {
 
     event SeedChanged(string btcAddr1, string btcAddr2, string hrp);
@@ -35,6 +45,9 @@ contract BTCDepositAddressDeriver {
 
         networkHrp = _hrp;
 
+        (p1x, p1y) = parseBTCTaprootAddress(_hrp, _btcAddr1);
+        (p2x, p2y) = parseBTCTaprootAddress(_hrp, _btcAddr2);
+
         btcAddr1 = _btcAddr1;
         btcAddr2 = _btcAddr2;
 
@@ -61,4 +74,31 @@ contract BTCDepositAddressDeriver {
 
         return _hrp;
     }
+
+    // Derive pubkey's (x,y) coordinates from taproot address
+    function parseBTCTaprootAddress(
+        string memory _hrp,
+        string calldata _bitcoinAddress
+    ) public pure returns (uint256, uint256) {
+
+        (uint8 witVer, bytes memory witProg, Bech32m.DecodeError err) = Bech32m
+            .decodeSegwitAddress(bytes(_hrp), bytes(_bitcoinAddress));
+
+        if (err != Bech32m.DecodeError.NoError) {
+            revert CannotParseBtcAddress(_bitcoinAddress, _hrp, err);
+        }
+        if (witVer != 1 || witProg.length != 32) {
+            revert UnsupportedBtcAddress(_bitcoinAddress);
+        }
+
+        uint256 x = uint256(bytes32(witProg));
+
+        if (x == 0 || x >= Deriver.PP) {
+            revert UnsupportedBtcAddress(_bitcoinAddress);
+        }
+
+        uint256 y = Deriver.liftX(x);
+
+        return (x, y);
+    }
 }