classification
Title: c_uint32 bitfields break structures
Type: behavior Stage:
Components: ctypes Versions: Python 2.7
process
Status: open Resolution:
Dependencies: Superseder:
Assigned To: Nosy List: Rony Batista, ned.deily, ronaldoussoren
Priority: normal Keywords:

Created on 2015-05-26 19:02 by Rony Batista, last changed 2015-05-27 22:57 by Rony Batista.

Files
File name Uploaded Description Edit
ctypesBug.py Rony Batista, 2015-05-26 19:06
Messages (5)
msg244125 - (view) Author: Rony Batista (Rony Batista) Date: 2015-05-26 19:02
ctypes Structures with c_uint32 bitfields have strange behaviour on OS X.

In the attached code when the field "number" is set, it changes the whole 32 bits, even thou its meant to be 23 bits.

The behavior is unexpected in:
OS X: Python 2.7.9

The behavior is as expected in the following environments:
Windows: python 2.7.9
Ubuntu: python 2.7.6
msg244126 - (view) Author: Ronald Oussoren (ronaldoussoren) * (Python committer) Date: 2015-05-26 19:04
You forgot to actually attach the code.
msg244127 - (view) Author: Rony Batista (Rony Batista) Date: 2015-05-26 19:06
Silly me, Heres the code.
msg244132 - (view) Author: Ned Deily (ned.deily) * (Python committer) Date: 2015-05-26 20:22
Without diving into the details of your test program, I get the same results on a 64-bit Debian Python 2.7.9 as with a 64-bit OS X 2.7.10:

c_uint32 TESTS:
Class Name		exponent 	number 	Sign 	float 				binary repr
IEEE754Float_u ('-0x7b', '0xbeb2aL', 0L, 69.95930480957031, ['0x42', '0x8b', '0xeb', '0x2a'])
IEEE754Float_u ('-0x7b', '0xbeb2aL', 0L, 69.95930480957031, ['0x42', '0x8b', '0xeb', '0x2a'])
AN575Float_uint ('0x0', '0xbeb2a', 0L, 1.094551427887186e-39, ['0x0', '0xb', '0xeb', '0x2a'])
AN575Float_uint ('0x0', '0xbeb2a', 0L, 1.094551427887186e-39, ['0x0', '0xb', '0xeb', '0x2a'])
AN575Float_uint ('-0x7b', '0xbeb2a', 0L, 1.094551427887186e-39, ['0x85', '0xb', '0xeb', '0x2a'])
IEEE754Float_u ('-0x7b', '0xbeb2aL', 1L, -69.95930480957031, ['0xc2', '0x8b', '0xeb', '0x2a'])
AN575Float_uint ('-0x7b', '0xbeb2a', 1L, 1.094551427887186e-39, ['0x85', '0x8b', '0xeb', '0x2a'])

But using the same OS X 2.7.10 in 32-bit mode, I get:

c_uint32 TESTS:
Class Name		exponent 	number 	Sign 	float 				binary repr
IEEE754Float_u ('-0x7b', '0xbeb2aL', 0L, 69.95930480957031, ['0x42', '0x8b', '0xeb', '0x2a'])
IEEE754Float_u ('-0x7b', '0xbeb2aL', 0L, 69.95930480957031, ['0x42', '0x8b', '0xeb', '0x2a'])
AN575Float_uint ('-0x7b', '0xbeb2a', 0L, 69.95930480957031, ['0x85', '0xb', '0xeb', '0x2a'])
AN575Float_uint ('-0x7b', '0xbeb2a', 0L, 69.95930480957031, ['0x85', '0xb', '0xeb', '0x2a'])
AN575Float_uint ('-0x7b', '0xbeb2a', 0L, 69.95930480957031, ['0x85', '0xb', '0xeb', '0x2a'])
IEEE754Float_u ('-0x7b', '0xbeb2aL', 1L, -69.95930480957031, ['0xc2', '0x8b', '0xeb', '0x2a'])
AN575Float_uint ('-0x7b', '0xbeb2a', 1L, -69.95930480957031, ['0x85', '0x8b', '0xeb', '0x2a'])
msg244223 - (view) Author: Rony Batista (Rony Batista) Date: 2015-05-27 22:57
Well, looks like the issue is with 64 bit mode then.

For the first 5 cases the right answer is 69.95930480957031, and for the last 2 its -69.95930480957031. The results for the 32 bit mode are all correct.
History
Date User Action Args
2015-05-27 22:57:25Rony Batistasetmessages: + msg244223
2015-05-26 20:22:05ned.deilysetnosy: + ned.deily
messages: + msg244132
2015-05-26 19:06:18Rony Batistasetfiles: + ctypesBug.py

messages: + msg244127
2015-05-26 19:04:35ronaldoussorensetnosy: + ronaldoussoren
messages: + msg244126
2015-05-26 19:02:48Rony Batistacreate