New submission from Marc Le Roy <mleroy...@gmail.com>:
The structure :
typedef struct __attribute__ ((packed)) {
unsigned int F0:24;
unsigned int F3:24;
unsigned int F6:24;
unsigned int F9:24;
} StructF_T;
is mapped as expected by GCC under both Linux and Cygwin.
As expected, the memory layout seen by the C program is :
0x111111222222333333444444
Using this definition :
class StructF(ctypes.BigEndianStructure):
_pack_ = 1
_fields_ = [
('F0', ctypes.c_uint, 24),
('F3', ctypes.c_uint, 24),
('F6', ctypes.c_uint, 24),
('F9', ctypes.c_uint, 24),
]
The memory layout seen from Python is not consistent :
0x11111100222222003333330044444400
It seems that the pack option is ignored by ctypes in such a case.
I found the same problem using both ctypes.BigEndianStructure and
ctypes.LittleEndianStructure
----------
components: ctypes
messages: 305914
nosy: mleroy003
priority: normal
severity: normal
status: open
title: Ctypes Packing Bitfields Incorrectly - GCC both Linux and Cygwin
versions: Python 3.6
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue31987>
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