c_uint32 bitfields break structures #68478
Comments
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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: The behavior is as expected in the following environments: |
RonyBatista
mannequin
added
topic-ctypes
type-bug
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You forgot to actually attach the code. |
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Silly me, Heres the code. |
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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: But using the same OS X 2.7.10 in 32-bit mode, I get: c_uint32 TESTS: |
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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. |
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Should be fixed in #97702. Code updated for Python 3: __author__ = 'rony'
from ctypes import BigEndianStructure
from ctypes import sizeof, memmove, addressof
from ctypes import c_int32, c_uint32
from struct import pack, unpack
class BigEndianByteStructure(BigEndianStructure):
# https://wiki.python.org/moin/ctypes
@classmethod
def from_bytes(cls, ibytes):
return_val = cls()
if len(ibytes) != sizeof(return_val):
raise ValueError(
'{0} Cannot unpack {2} bytes, it should be {1} bytes'.format(cls.__name__, sizeof(return_val),
len(ibytes)))
memmove(addressof(return_val), ibytes, len(ibytes))
return return_val
@classmethod
def from_structure(cls, original):
return_val = cls()
for field in return_val._fields_:
try:
setattr(return_val, field[0], getattr(original, field[0]))
except:
print( 'Attribute {0} not found in original'.format(field[0]))
return return_val
# POSITIVE
# IEEE754 HEX 0x428beb2a
# AN575 HEX 0x850beb2a
# NEGATIVE
# IEEE754 HEX 0xc28beb2a
# AN575 HEX 0x858beb2a
class IEEE754Float(BigEndianByteStructure):
_pack_ = 1
_fields_ = [('sign', c_int32, 1),
('exponent', c_int32, 8),
('number', c_int32, 23)]
@classmethod
def from_float(cls, f):
return cls.from_bytes(pack('>f', f))
def __float__(self):
return unpack('>f', memoryview(self))[0]
def debug(self):
f = self
return hex(f.exponent), hex(f.number), f.sign, float(f), [hex(b) for b in bytearray(f)]
class AN575Float(BigEndianByteStructure):
_pack_ = 1
_fields_ = [('exponent', c_int32, 8),
('sign', c_int32, 1),
('number', c_int32, 23)]
@classmethod
def from_float(cls, f):
return cls.from_structure(IEEE754Float.from_float(f))
def __float__(self):
a = IEEE754Float.from_structure(self)
return float(a)
def debug(self):
f = self
return hex(f.exponent), hex(f.number), f.sign, float(f), [hex(b) for b in bytearray(f)]
class IEEE754Float_u(BigEndianByteStructure):
_pack_ = 1
_fields_ = [('sign', c_uint32, 1),
('exponent', c_int32, 8),
('number', c_uint32, 23)]
@classmethod
def from_float(cls, f):
return cls.from_bytes(pack('>f', f))
def __float__(self):
return unpack('>f', memoryview(self))[0]
def debug(self):
f = self
return hex(f.exponent), hex(f.number), f.sign, float(f), [hex(b) for b in bytearray(f)]
class AN575Float_uint(BigEndianByteStructure):
_pack_ = 1
_fields_ = [('exponent', c_int32, 8),
('sign', c_uint32, 1),
('number', c_int32, 23)]
@classmethod
def from_float(cls, f):
return cls.from_structure(IEEE754Float_u.from_float(f))
def __float__(self):
a = IEEE754Float_u.from_structure(self)
return float(a)
def debug(self):
f = self
return hex(f.exponent), hex(f.number), f.sign, float(f), [hex(b) for b in bytearray(f)]
print ('\n', 'c_int32 TESTS:')
print ('Class Name\t\t', 'exponent', '\tnumber', '\tSign', '\tfloat', '\t\t\t\t', 'binary repr')
f = IEEE754Float.from_float(69.9593067)
print (type(f).__name__, f.debug())
f = IEEE754Float.from_bytes(b'\x42\x8b\xeb\x2a')
print (type(f).__name__, f.debug())
f = AN575Float.from_float(69.9593067)
print (type(f).__name__, f.debug())
f = AN575Float.from_structure(IEEE754Float.from_float(69.9593067))
print (type(f).__name__, f.debug())
f = AN575Float.from_bytes(b'\x85\x0b\xeb\x2a')
print (type(f).__name__, f.debug())
f = IEEE754Float.from_bytes(b'\xc2\x8b\xeb\x2a')
print (type(f).__name__, f.debug())
f = AN575Float.from_bytes(b'\x85\x8b\xeb\x2a')
print (type(f).__name__, f.debug())
print ('\n', 'c_uint32 TESTS:')
print ('Class Name\t\t', 'exponent', '\tnumber', '\tSign', '\tfloat', '\t\t\t\t', 'binary repr')
f = IEEE754Float_u.from_float(69.9593067)
print (type(f).__name__, f.debug())
f = IEEE754Float_u.from_bytes(b'\x42\x8b\xeb\x2a')
print (type(f).__name__, f.debug())
f = AN575Float_uint.from_float(69.9593067)
print (type(f).__name__, f.debug())
f = AN575Float_uint.from_structure(IEEE754Float.from_float(69.9593067))
print (type(f).__name__, f.debug())
f = AN575Float_uint.from_bytes(b'\x85\x0b\xeb\x2a')
print (type(f).__name__, f.debug())
f = IEEE754Float_u.from_bytes(b'\xc2\x8b\xeb\x2a')
print (type(f).__name__, f.debug())
f = AN575Float_uint.from_bytes(b'\x85\x8b\xeb\x2a')
print (type(f).__name__, f.debug())Result (same on 64- and 32-bit OS): |
Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.
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