Optimise float(int).

Cython/Utility/TypeConversion.c

@@ -474,20 +474,43 @@ static CYTHON_INLINE PyObject* __Pyx__PyNumber_Float(PyObject* obj); /* proto */
 //@requires: Optimize.c::pyunicode_as_double
 
 static CYTHON_INLINE PyObject* __Pyx__PyNumber_Float(PyObject* obj) {
-    // obj is PyFloat is handled in the calling macro
+    // 'obj is PyFloat' is handled in the calling macro
     double val;
-    if (PyUnicode_CheckExact(obj)) {
+    if (PyLong_CheckExact(obj)) {
+#if CYTHON_USE_PYLONG_INTERNALS
+        const digit* digits = ((PyLongObject*)obj)->ob_digit;
+        switch (Py_SIZE(obj)) {
+            case 0:
+                val = 0.0;
+                goto no_error;
+            // single digit PyLong values always cast safely to double
+            case 1:
+                val = (double) digits[0];
+                goto no_error;
+            case -1:
+                val = (double) - (sdigit) digits[0];
+                goto no_error;
+            default:
+                val = PyLong_AsDouble(obj);
+        }
+#else
+        val = PyLong_AsDouble(obj);
+#endif
+    } else if (PyUnicode_CheckExact(obj)) {
         val = __Pyx_PyUnicode_AsDouble(obj);
-        return unlikely(val == -1 && PyErr_Occurred()) ? NULL : PyFloat_FromDouble(val);
     } else if (PyBytes_CheckExact(obj)) {
         val = __Pyx_PyBytes_AsDouble(obj);
-        return unlikely(val == -1 && PyErr_Occurred()) ? NULL : PyFloat_FromDouble(val);
     } else if (PyByteArray_CheckExact(obj)) {
         val = __Pyx_PyByteArray_AsDouble(obj);
-        return unlikely(val == -1 && PyErr_Occurred()) ? NULL : PyFloat_FromDouble(val);
     } else {
         return PyNumber_Float(obj);
     }
+
+    if (unlikely(val == -1 && PyErr_Occurred())) {
+        return NULL;
+    }
+no_error:
+    return PyFloat_FromDouble(val);
 }
 
 /////////////// GCCDiagnostics.proto ///////////////

tests/run/builtin_float.py

@@ -44,6 +44,29 @@ def float_call_conjugate():
     return x
 
 
+def from_int(i):
+    """
+    >>> from_int(0)
+    0.0
+    >>> from_int(1)
+    1.0
+    >>> from_int(-1)
+    -1.0
+    >>> from_int(99)
+    99.0
+    >>> from_int(-99)
+    -99.0
+
+    >>> for exp in (14, 15, 16, 30, 31, 32, 52, 53, 54, 60, 61, 62, 63, 64):
+    ...     for sign in (1, 0, -1):
+    ...         value = (sign or 1) * 2**exp + sign
+    ...         float_value = from_int(value)
+    ...         assert float_value == float(value), "expected %s2**%s+%s == %r, got %r, difference %r" % (
+    ...             '-' if sign < 0 else '', exp, sign, float(value), float_value, float_value - float(value))
+    """
+    return float(i)
+
+
 @cython.test_assert_path_exists(
     "//CoerceToPyTypeNode",
     "//CoerceToPyTypeNode//PythonCapiCallNode",