feat: add ADF (Augmented Dickey-Fuller) indicator

- Core implementation with Cholesky OLS, MacKinnon p-value, AIC lag selection
- Three regression models: NoConstant, Constant, ConstantAndTrend
- NormCdf via Abramowitz & Stegun 7.1.26 erf approximation
- Quantower adapter, Python bridge (NativeAOT export + ctypes + wrapper)
- 69 tests (41 unit + 12 validation + 14 Quantower + 2 consistency)
- Documentation with Schwert table, MacKinnon coefficients, PineScript ref
- All 19,095 tests pass, zero warnings

python/quantalib/_bridge.py

@@ -254,6 +254,7 @@ HAS_WAD = _bind("qtl_wad", [_dp, _dp, _dp, _dp, _dp, _ci])
 # ═══════════════════════════════════════════════════════════════════════════
 #  Statistics
 # ═══════════════════════════════════════════════════════════════════════════
+HAS_ADF = _bind("qtl_adf", [_dp, _dp, _ci, _ci, _ci, _ci])
 HAS_ACF = _bind("qtl_acf", [_dp, _dp, _ci, _ci, _ci])
 HAS_GEOMEAN = _bind("qtl_geomean", [_dp, _dp, _ci, _ci])
 HAS_GRANGER = _bind("qtl_granger", [_dp, _dp, _dp, _ci, _ci])

python/quantalib/statistics.py

@@ -8,6 +8,7 @@ from ._helpers import _arr, _ptr, _out, _wrap, _wrap_multi, _check, _lib
 
 
 __all__ = [
+    "adf",
     "acf",
     "geomean",
     "granger",
@@ -43,6 +44,19 @@ __all__ = [
 ]
 
 
+def adf(close: object, period: int = 50, max_lag: int = 0, regression: int = 1, offset: int = 0, **kwargs) -> object:
+    """Augmented Dickey-Fuller test p-value."""
+    period = int(kwargs.get("length", period))
+    max_lag = int(max_lag)
+    regression = int(regression)
+    offset = int(offset)
+    src, idx = _arr(close)
+    n = len(src)
+    output = _out(n)
+    _check(_lib.qtl_adf(_ptr(src), _ptr(output), n, period, max_lag, regression))
+    return _wrap(output, idx, f"ADF_{period}", "statistics", offset)
+
+
 def acf(close: object, period: int = 14, lag: int = 10, offset: int = 0, **kwargs) -> object:
     """Autocorrelation Function."""
     period = int(kwargs.get("length", period))

python/src/Exports.Generated.cs

@@ -105,6 +105,19 @@ public static unsafe partial class Exports
         catch { return StatusCodes.QTL_ERR_INTERNAL; }
     }
 
+    [UnmanagedCallersOnly(EntryPoint = "qtl_adf")]
+    public static int QtlAdf(double* source, double* output, int n, int period, int maxLag, int regression)
+    {
+        if (source == null || output == null) return StatusCodes.QTL_ERR_NULL_PTR;
+        if (n <= 0) return StatusCodes.QTL_ERR_INVALID_LENGTH;
+        try
+        {
+            Adf.Batch(Src(source, n), Dst(output, n), period, maxLag, (Adf.AdfRegression)regression);
+            return StatusCodes.QTL_OK;
+        }
+        catch { return StatusCodes.QTL_ERR_INTERNAL; }
+    }
+
     [UnmanagedCallersOnly(EntryPoint = "qtl_adl")]
     public static int QtlAdl(double* high, double* low, double* close, double* volume, double* output, int n)
     {