Issue #29282: add fused multiply-add function, math.fma.

Modules/clinic/mathmodule.c.h

@@ -80,6 +80,40 @@ PyDoc_STRVAR(math_factorial__doc__,
 #define MATH_FACTORIAL_METHODDEF    \
     {"factorial", (PyCFunction)math_factorial, METH_O, math_factorial__doc__},
 
+PyDoc_STRVAR(math_fma__doc__,
+"fma($module, x, y, z, /)\n"
+"--\n"
+"\n"
+"Fused multiply-add operation. Compute (x * y) + z with a single round.");
+
+#define MATH_FMA_METHODDEF    \
+    {"fma", (PyCFunction)math_fma, METH_FASTCALL, math_fma__doc__},
+
+static PyObject *
+math_fma_impl(PyObject *module, double x, double y, double z);
+
+static PyObject *
+math_fma(PyObject *module, PyObject **args, Py_ssize_t nargs, PyObject *kwnames)
+{
+    PyObject *return_value = NULL;
+    double x;
+    double y;
+    double z;
+
+    if (!_PyArg_ParseStack(args, nargs, "ddd:fma",
+        &x, &y, &z)) {
+        goto exit;
+    }
+
+    if (!_PyArg_NoStackKeywords("fma", kwnames)) {
+        goto exit;
+    }
+    return_value = math_fma_impl(module, x, y, z);
+
+exit:
+    return return_value;
+}
+
 PyDoc_STRVAR(math_trunc__doc__,
 "trunc($module, x, /)\n"
 "--\n"
@@ -536,4 +570,4 @@ math_isclose(PyObject *module, PyObject **args, Py_ssize_t nargs, PyObject *kwna
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=71806f73a5c4bf0b input=a9049054013a1b77]*/
+/*[clinic end generated code: output=f428e1075d00c334 input=a9049054013a1b77]*/

Modules/mathmodule.c

@@ -1595,6 +1595,47 @@ math_factorial(PyObject *module, PyObject *arg)
 }
 
 
+/*[clinic input]
+math.fma
+
+    x: double
+    y: double
+    z: double
+    /
+
+Fused multiply-add operation. Compute (x * y) + z with a single round.
+[clinic start generated code]*/
+
+static PyObject *
+math_fma_impl(PyObject *module, double x, double y, double z)
+/*[clinic end generated code: output=4fc8626dbc278d17 input=2ae8bb2a6e0f8b77]*/
+{
+    double r;
+    r = fma(x, y, z);
+
+    /* Fast path: if we got a finite result, we're done. */
+    if (Py_IS_FINITE(r)) {
+        return PyFloat_FromDouble(r);
+    }
+
+    /* Non-finite result. Raise an exception if appropriate, else return r. */
+    if (Py_IS_NAN(r)) {
+        if (!Py_IS_NAN(x) && !Py_IS_NAN(y) && !Py_IS_NAN(z)) {
+            /* NaN result from non-NaN inputs. */
+            PyErr_SetString(PyExc_ValueError, "invalid operation in fma");
+            return NULL;
+        }
+    }
+    else if (Py_IS_FINITE(x) && Py_IS_FINITE(y) && Py_IS_FINITE(z)) {
+        /* Infinite result from finite inputs. */
+        PyErr_SetString(PyExc_OverflowError, "overflow in fma");
+        return NULL;
+    }
+
+    return PyFloat_FromDouble(r);
+}
+
+
 /*[clinic input]
 math.trunc
 
@@ -2224,6 +2265,7 @@ static PyMethodDef math_methods[] = {
     {"fabs",            math_fabs,      METH_O,         math_fabs_doc},
     MATH_FACTORIAL_METHODDEF
     MATH_FLOOR_METHODDEF
+    MATH_FMA_METHODDEF
     MATH_FMOD_METHODDEF
     MATH_FREXP_METHODDEF
     MATH_FSUM_METHODDEF