Guido suggests, and I agree, to insist that SIZEOF_VOID_P be a power of 2.
This simplifies the rounding in _PyObject_VAR_SIZE, allows to restore the
pre-rounding calling sequence, and allows some nice little simplifications
in its callers. I'm still making it return a size_t, though.
diff --git a/Include/objimpl.h b/Include/objimpl.h
index 2ea3ad5..db4cb6d 100644
--- a/Include/objimpl.h
+++ b/Include/objimpl.h
@@ -173,40 +173,36 @@
#define _PyObject_SIZE(typeobj) ( (typeobj)->tp_basicsize )
-/* _PyObject_VAR_SIZE computes the amount of memory allocated for a vrbl-
- size object with nitems items, exclusive of gc overhead (if any). The
- value is rounded up to the closest multiple of sizeof(void *), in order
- to ensure that pointer fields at the end of the object are correctly
- aligned for the platform (this is of special importance for subclasses
- of, e.g., str or long, so that pointers can be stored after the embedded
- data).
+/* _PyObject_VAR_SIZE returns the number of bytes (as size_t) allocated for a
+ vrbl-size object with nitems items, exclusive of gc overhead (if any). The
+ value is rounded up to the closest multiple of sizeof(void *), in order to
+ ensure that pointer fields at the end of the object are correctly aligned
+ for the platform (this is of special importance for subclasses of, e.g.,
+ str or long, so that pointers can be stored after the embedded data).
- Note that there's no memory wastage in doing this, as malloc has to
- return (at worst) pointer-aligned memory anyway
-
- However, writing the macro to *return* the result is clumsy due to the
- calculations needed. Instead you must pass the result lvalue as the first
- argument, and it should be of type size_t (both because that's the
- correct conceptual type, and because using an unsigned type allows the
- compiler to generate faster code for the mod computation inside the
- macro).
+ Note that there's no memory wastage in doing this, as malloc has to
+ return (at worst) pointer-aligned memory anyway.
*/
-#define _PyObject_VAR_SIZE(result, typeobj, nitems) \
- do { \
- size_t mod; \
- (result) = (size_t) (typeobj)->tp_basicsize; \
- (result) += (size_t) ((nitems)*(typeobj)->tp_itemsize); \
- mod = (result) % SIZEOF_VOID_P; \
- if (mod) \
- (result) += SIZEOF_VOID_P - mod; \
- } while(0)
+#if ((SIZEOF_VOID_P - 1) & SIZEOF_VOID_P) != 0
+# error "_PyObject_VAR_SIZE requires SIZEOF_VOID_P be a power of 2"
+#endif
+
+#define _PyObject_VAR_SIZE(typeobj, nitems) \
+ (size_t) \
+ ( ( (typeobj)->tp_basicsize + \
+ (nitems)*(typeobj)->tp_itemsize + \
+ (SIZEOF_VOID_P - 1) \
+ ) & ~(SIZEOF_VOID_P - 1) \
+ )
#define PyObject_NEW(type, typeobj) \
( (type *) PyObject_Init( \
(PyObject *) PyObject_MALLOC( _PyObject_SIZE(typeobj) ), (typeobj)) )
-#define PyObject_NEW_VAR(type, typeobj, nitems) \
- ((type *) _PyObject_NewVar(typeobj, nitems))
+#define PyObject_NEW_VAR(type, typeobj, n) \
+( (type *) PyObject_InitVar( \
+ (PyVarObject *) PyObject_MALLOC(_PyObject_VAR_SIZE((typeobj),(n)) ),\
+ (typeobj), (n)) )
#define PyObject_DEL(op) PyObject_FREE(op)