1 files changed, 30 insertions, 0 deletions
diff --git a/Modules/_testcapi/float.c b/Modules/_testcapi/float.c
index e386913..2feeb20 100644
--- a/Modules/_testcapi/float.c
+++ b/Modules/_testcapi/float.c
@@ -157,9 +157,39 @@ test_string_to_double(PyObject *self, PyObject *Py_UNUSED(ignored))
 }
 
 
+/*[clinic input]
+_testcapi.float_set_snan
+
+    obj: object
+    /
+
+Make a signaling NaN.
+[clinic start generated code]*/
+
+static PyObject *
+_testcapi_float_set_snan(PyObject *module, PyObject *obj)
+/*[clinic end generated code: output=f43778a70f60aa4b input=c1269b0f88ef27ac]*/
+{
+    if (!PyFloat_Check(obj)) {
+        PyErr_SetString(PyExc_ValueError, "float-point number expected");
+        return NULL;
+    }
+    double d = ((PyFloatObject *)obj)->ob_fval;
+    if (!isnan(d)) {
+        PyErr_SetString(PyExc_ValueError, "nan expected");
+        return NULL;
+    }
+    uint64_t v;
+    memcpy(&v, &d, 8);
+    v &= ~(1ULL << 51); /* make sNaN */
+    memcpy(&d, &v, 8);
+    return PyFloat_FromDouble(d);
+}
+
 static PyMethodDef test_methods[] = {
     _TESTCAPI_FLOAT_PACK_METHODDEF
     _TESTCAPI_FLOAT_UNPACK_METHODDEF
+    _TESTCAPI_FLOAT_SET_SNAN_METHODDEF
     {"test_string_to_double", test_string_to_double, METH_NOARGS},
     {NULL},
 };