marginal price views

src/LMSRStabilized.sol

@@ -778,6 +778,51 @@ library LMSRStabilized {
         return e_i_acc.div(Z);
     }
 
+    /// @notice Marginal price of `base` in terms of `quote` (p_quote / p_base) as Q64.64
+    /// @dev Returns exp((q_quote - q_base) / b). Indices must be valid and b > 0.
+    function price(State storage s, uint256 baseTokenIndex, uint256 quoteTokenIndex) internal view returns (int128) {
+        require(baseTokenIndex < s.nAssets && quoteTokenIndex < s.nAssets, "LMSR: idx");
+        int128 b = _computeB(s);
+        require(b > int128(0), "LMSR: b<=0");
+
+        // Use reciprocal of b to avoid repeated divisions
+        int128 invB = ABDKMath64x64.div(ONE, b);
+
+        // Marginal price p_quote / p_base = exp((q_quote - q_base) / b)
+        return _exp(s.qInternal[quoteTokenIndex].sub(s.qInternal[baseTokenIndex]).mul(invB));
+    }
+
+    /// @notice Price of one unit of the LP size-metric (S = sum q_i) denominated in `quote` asset (Q64.64)
+    /// @dev Computes: poolPrice_quote = (1 / S) * sum_j q_j * exp((q_j - q_quote) / b)
+    function poolPrice(State storage s, uint256 quoteTokenIndex) internal view returns (int128) {
+        require(quoteTokenIndex < s.nAssets, "LMSR: idx");
+        // Compute b and ensure positivity
+        int128 b = _computeB(s);
+        require(b > int128(0), "LMSR: b<=0");
+
+        // Compute total size metric S = sum q_i
+        int128 S = _computeSizeMetric(s.qInternal);
+        require(S > int128(0), "LMSR: size zero");
+
+        // Precompute reciprocal of b
+        int128 invB = ABDKMath64x64.div(ONE, b);
+
+        // Accumulate weighted exponentials: sum_j q_j * exp((q_j - q_quote) / b)
+        int128 acc = int128(0);
+        uint256 n = s.nAssets;
+        for (uint256 j = 0; j < n; ) {
+            // factor = exp((q_j - q_quote) / b)
+            int128 factor = _exp(s.qInternal[j].sub(s.qInternal[quoteTokenIndex]).mul(invB));
+            // term = q_j * factor
+            int128 term = s.qInternal[j].mul(factor);
+            acc = acc.add(term);
+            unchecked { j++; }
+        }
+
+        // pool price in units of quote = (1 / S) * acc
+        return acc.div(S);
+    }
+
     /* --------------------
        Slippage -> b computation & resize-triggered rescale
        -------------------- */