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

1 files changed, 42 insertions, 0 deletions

diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
index 8bd38d0..66e88b6 100644
--- a/Modules/mathmodule.c
+++ b/Modules/mathmodule.c
@@ -1596,6 +1596,47 @@ 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
 
     x: object
@@ -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