🐛 point unicity in validity check

src/ECDSA256r1.sol

@@ -19,7 +19,7 @@
     /// @param y The y-coordinate of the point
     /// @return bool True if the point is on the curve, false otherwise
     function isPointValid(uint256 x, uint256 y) internal pure returns (bool) {
-        if (((0 == x) && (0 == y)) || x == p || y == p) {
+        if ((0 == x % p) && (0 == y % p)) {
             return false;
         }
 
@@ -42,14 +42,14 @@
     /// @param scalar_u Multiplier for basepoint G
     /// @param scalar_v Multiplier for input point Q
     /// @return X Resulting x-coordinate of the computed point
     function mulmuladd(uint256 Q0, uint256 Q1, uint256 scalar_u, uint256 scalar_v) internal returns (uint256 X) {
         uint256 zz;
         uint256 zzz;
         uint256 Y;
         uint256 index = 255;
         uint256[6] memory T;
         uint256 H0;
         uint256 H1;
 
         unchecked {
             if (scalar_u == 0 && scalar_v == 0) return 0;
@@ -57,7 +57,7 @@
             // will not work if Q=P, obvious forbidden private key
             (H0, H1) = ECDSA.affAdd(gx, gy, Q0, Q1);
 
             assembly {
                 for { let T4 := add(shl(1, and(shr(index, scalar_v), 1)), and(shr(index, scalar_u), 1)) } eq(T4, 0) {
                     index := sub(index, 1)
                     T4 := add(shl(1, and(shr(index, scalar_v), 1)), and(shr(index, scalar_u), 1))