[ python-Bugs-1575945 ] from_param and _as_parameter_ truncating 64-bit value

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Bugs item #1575945, was opened at 2006-10-12 16:25
Message generated for change (Comment added) made by albertstrasheim
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Category: Python Library
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Albert Strasheim (albertstrasheim)
Assigned to: Thomas Heller (theller)
Summary: from_param and _as_parameter_ truncating 64-bit value

Initial Comment:
There seems to be something strange going on with
ctypes' _as_parameter_ on 64-bit machines. I haven't
been able to replicate this problem without NumPy, but
it looks like a ctypes issue since NumPy's
_as_parameter_ contains a valid value but the value
that arrives in the C function has had its upper 4
bytes zeroed.

SConstruct to build library:

env = Environment()
env.Replace(CCFLAGS=['-O0','-ggdb','-Wall','-ansi','-pedantic'])
env.SharedLibrary('spfuncs',['spfuncs.c'])

C code:

#include <stdio.h>
void nnz(double *ary) {
    printf("ary = %p\n", (void*)ary);
}

Python code:

import numpy as N
from ctypes import *
from numpy.ctypeslib import ndpointer
_libspfuncs = N.ctypeslib.load_library('libspfuncs',
__file__) _libspfuncs.nnz.restype  = None A =
N.eye((128)) print 'data_as',
A.ctypes.data_as(c_void_p) print 'array interface',
hex(A.__array_interface__['data'][0])
_libspfuncs.nnz.argtypes = [POINTER(c_double)]
_libspfuncs.nnz(A.ctypes.data_as(POINTER(c_double)))
_libspfuncs.nnz.argtypes = [ndpointer(dtype = N.float64)]
_libspfuncs.nnz(A)
print '_as_parameter', hex(A.ctypes._as_parameter_)

Output on 32-bit system:

data_as c_void_p(-1212006392)
array interface -0x483dbff8
ary = 0xb7c24008
ary = 0xb7c24008
_as_parameter -0x483dbff8

Output on 64-bit system:

data_as c_void_p(46912559644688)
array interface 0x2aaaae740010
ary = 0x2aaaae740010
ary = 0xae740010
_as_parameter 0x2aaaae740010

----------------------------------------------------------------------

>Comment By: Albert Strasheim (albertstrasheim)
Date: 2006-10-16 18:18

Message:
Logged In: YES 
user_id=945096

Changing NumPy's _as_parameter_ to return the pointer as a
c_void_p causes ctypes to raise the following erorr:

ctypes.ArgumentError: argument 1: exceptions.TypeError:
Don't know how to convert parameter 1

----------------------------------------------------------------------

Comment By: Thomas Heller (theller)
Date: 2006-10-16 17:05

Message:
Logged In: YES 
user_id=11105

This is not a ctypes bug.

It seems that A.ctypes._as_parameter_ is a Python integer. 
These are passed as 'C int' type to foreign function calls.
(The C int type typically has 32 bits on 64-bit platforms,
while a pointer has 64 bit.)

To pass a pointer, A.ctypes._as_parameter_ should be a
ctypes c_void_p instance, not a Python integer.

----------------------------------------------------------------------

Comment By: Martin v. Löwis (loewis)
Date: 2006-10-14 22:07

Message:
Logged In: YES 
user_id=21627

Thomas, can you take a look? If not, please unassign.

----------------------------------------------------------------------

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