Revert "XXX try PyLong_Export without value"

This reverts commit bf687e5.

Author: skirpichev

Modules/_decimal/_decimal.c

@@ -2335,17 +2335,9 @@ dec_from_long(decimal_state *state, PyTypeObject *type, PyObject *v,
         return NULL;
     }
     if (export_long.digits) {
-        const uint8_t sign = export_long.negative ? MPD_NEG : MPD_POS;
-
-        if (PyUnstable_Long_IsCompact((PyLongObject *)v)) {
-            _dec_settriple(dec, sign, ((uint32_t *)export_long.digits)[0], 0);
-            mpd_qfinalize(MPD(dec), ctx, status);
-            PyLong_FreeExport(&export_long);
-            return dec;
-        }
-
         const PyLongLayout *layout = PyLong_GetNativeLayout();
         const uint32_t base = (uint32_t)1 << layout->bits_per_digit;
+        const uint8_t sign = export_long.negative ? MPD_NEG : MPD_POS;
         const Py_ssize_t len = export_long.ndigits;
 
         if (base > UINT16_MAX) {

Objects/longobject.c

@@ -6842,15 +6842,36 @@ PyLong_Export(PyObject *obj, PyLongExport *export_long)
         return -1;
     }
 
-    PyLongObject *self = (PyLongObject*)obj;
-    export_long->value = 0;
-    export_long->negative = _PyLong_IsNegative(self);
-    export_long->ndigits = _PyLong_DigitCount(self);
-    if (export_long->ndigits == 0) {
-        export_long->ndigits = 1;
-    }
-    export_long->digits = self->long_value.ob_digit;
-    export_long->_reserved = (Py_uintptr_t)Py_NewRef(obj);
+    // Fast-path: try to convert to a int64_t
+    int overflow;
+#if SIZEOF_LONG == 8
+    long value = PyLong_AsLongAndOverflow(obj, &overflow);
+#else
+    // Windows has 32-bit long, so use 64-bit long long instead
+    long long value = PyLong_AsLongLongAndOverflow(obj, &overflow);
+#endif
+    Py_BUILD_ASSERT(sizeof(value) == sizeof(int64_t));
+    // the function cannot fail since obj is a PyLongObject
+    assert(!(value == -1 && PyErr_Occurred()));
+
+    if (!overflow) {
+        export_long->value = value;
+        export_long->negative = 0;
+        export_long->ndigits = 0;
+        export_long->digits = NULL;
+        export_long->_reserved = 0;
+    }
+    else {
+        PyLongObject *self = (PyLongObject*)obj;
+        export_long->value = 0;
+        export_long->negative = _PyLong_IsNegative(self);
+        export_long->ndigits = _PyLong_DigitCount(self);
+        if (export_long->ndigits == 0) {
+            export_long->ndigits = 1;
+        }
+        export_long->digits = self->long_value.ob_digit;
+        export_long->_reserved = (Py_uintptr_t)Py_NewRef(obj);
+    }
     return 0;
 }