more volatilty

lib/core/simd/SimdExtensions.cs

@@ -174,6 +174,19 @@ public static class SimdExtensions
         return ContainsNonFiniteScalar(span);
     }
 
+    /// <summary>
+    /// Calculates sum using SIMD vectorization when available.
+    /// 4-8x faster than scalar loop on AVX2/AVX-512 hardware.
+    /// Returns NaN if any input value is non-finite.
+    /// Uses lazy non-finite check: computes sum first, then validates result.
+    /// If result is non-finite, falls back to explicit check.
+    /// </summary>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static double SumSIMD(this Span<double> span)
+    {
+        return SumSIMD((ReadOnlySpan<double>)span);
+    }
+
     /// <summary>
     /// Calculates sum using SIMD vectorization when available.
     /// 4-8x faster than scalar loop on AVX2/AVX-512 hardware.