bpo-42161: Add _PyLong_GetZero() and _PyLong_GetOne() (GH-22993)

Add _PyLong_GetZero() and _PyLong_GetOne() functions and a new
internal pycore_long.h header file.

Python cannot be built without small integer singletons anymore.

1 files changed, 43 insertions, 0 deletions

diff --git a/Include/internal/pycore_long.h b/Include/internal/pycore_long.h
new file mode 100644
index 0000000..ec95786
--- /dev/null
+++ b/Include/internal/pycore_long.h
@@ -0,0 +1,43 @@
+#ifndef Py_INTERNAL_LONG_H
+#define Py_INTERNAL_LONG_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef Py_BUILD_CORE
+#  error "this header requires Py_BUILD_CORE define"
+#endif
+
+#include "pycore_interp.h"        // PyInterpreterState.small_ints
+#include "pycore_pystate.h"       // _PyThreadState_GET()
+
+// Don't call this function but _PyLong_GetZero() and _PyLong_GetOne()
+static inline PyObject* __PyLong_GetSmallInt_internal(int value)
+{
+    PyThreadState *tstate = _PyThreadState_GET();
+#ifdef Py_DEBUG
+    _Py_EnsureTstateNotNULL(tstate);
+#endif
+    assert(-_PY_NSMALLNEGINTS <= value && value < _PY_NSMALLPOSINTS);
+    size_t index = _PY_NSMALLNEGINTS + value;
+    PyObject *obj = (PyObject*)tstate->interp->small_ints[index];
+    // _PyLong_GetZero() and _PyLong_GetOne() must not be called
+    // before _PyLong_Init() nor after _PyLong_Fini()
+    assert(obj != NULL);
+    return obj;
+}
+
+// Return a borrowed reference to the zero singleton.
+// The function cannot return NULL.
+static inline PyObject* _PyLong_GetZero(void)
+{ return __PyLong_GetSmallInt_internal(0); }
+
+// Return a borrowed reference to the one singleton.
+// The function cannot return NULL.
+static inline PyObject* _PyLong_GetOne(void)
+{ return __PyLong_GetSmallInt_internal(1); }
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* !Py_INTERNAL_LONG_H */