diff --git a/Objects/floatobject.c b/Objects/floatobject.c index 30f7b3489da..ba867ef149f 100644 --- a/Objects/floatobject.c +++ b/Objects/floatobject.c @@ -1088,6 +1088,15 @@ _Py_double_round(double x, int ndigits) { PyObject *result = NULL; _Py_SET_53BIT_PRECISION_HEADER; + /* Easy path for the common case ndigits == 0. */ + if (ndigits == 0) { + rounded = round(x); + if (fabs(rounded - x) == 0.5) + /* halfway between two integers; use round-away-from-zero */ + rounded = x + (x > 0.0 ? 0.5 : -0.5); + return PyFloat_FromDouble(rounded); + } + /* The basic idea is very simple: convert and round the double to a decimal string using _Py_dg_dtoa, then convert that decimal string back to a double with _Py_dg_strtod. There's one minor difficulty: