[Python-Dev] Type of range object members
"Martin v. Löwis"
martin at v.loewis.de
Thu Aug 17 08:27:02 CEST 2006
Neal Norwitz schrieb:
> It would change the CheckExact()s from: op->ob_type ==
> global-variable, to: op->ob_type & CONSTANT == CONSTANT. Check would
> be the same as the CheckExact, just with different constants. The
> Check version would then drop the || condition.
Hmm. I don't see the for the FAST_SUBCLASS bit still.
I would set the relevant bit in the type object itself, and then have
#define PyInt_CheckExact(op) ((op)->ob_type == &PyInt_Type)
#define PyInt_Check(op) \
Then, in inherit_special, I'd do
type->tp_flags |= base->tp_flags & Py_TPFLAGS_FAST_SUBCLASS_MASK;
So you would have a pointer comparison for the exact check, and the
bit mask check for the subtype check.
It's likely that the pointer comparison is still more efficient: It
does *not*, normally, need to read a global variable to get the address
Currently, on x86, with non-PIC code on Linux, the pointer check compiles as
cmpl $PyInt_Type, 4(%eax) ; %eax is the object
where the linker fills the address of PyInt_Type into the machine
instruction. OTOH, the access to the flags compiles as
movl 4(%eax), %eax ; %eax is the object
movl 84(%eax), %eax
andl $2013265920, %eax
cmpl $2013265920, %eax
Even with PIC code, the address check is still more efficient:
movl PyInt_Type at GOT(%ecx), %eax
cmpl %eax, 4(%edx) ; %edx is the object
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