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Notes |
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(0002729)
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Nicolas Savoire
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2005-07-27 11:55
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A similarly incorrect function is used in BilateralImageFilter. |
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(0002771)
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Lydia Ng
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2005-08-05 15:02
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Triaged 8/5/05 tcon.
Jim will look at it. |
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(0002810)
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Nicolas Savoire
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2005-08-08 03:45
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I forgot to add that the bug affects only the i386 platform.
Replacing
unsigned int hilo[2];
*((double *)hilo) = x + 103079215104.0;
return (int)((hilo[1]<<16)|(hilo[0]>>16));
by
union { unsigned int hilo[2]; double d; } u;
u.d = x + 103079215104.0;
return (int)((u.hilo[1]<<16)|(u.hilo[0]>>16));
seems to fix the problem.
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(0002917)
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Nicolas Savoire
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2005-08-18 08:12
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Another thing: the bug seems to appear only with gcc 3.4 and flag -O2/-O3 |
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(0003285)
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user390
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2005-11-20 23:34
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(0009206)
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Luis Ibanez
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2007-09-21 15:56
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correcting 'resolved' status to 'closed' |
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(0009269)
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Nicolas Savoire
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2007-09-24 02:44
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It seems that the returned value is wrong for inputs really close but smaller than a given integer:
BSplineFloor(0.999999) returns 1 instead of 0.
I think the issue is the addition of a large constant value which triggers a loss of precision. |
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(0009270)
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Luis Ibanez
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2007-09-24 08:34
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Nicos,
Can you please provide a test program that illustrate this problem ?
We need a test in order to track the issue.
Also, is it still the case that this error is only observed
in gcc 3.4 with flags -O2/O3 ?
For the long term maintenance it seems better to use vcl_floor().
Whether this is a performance issue or not, is something that we
have to verify by using a profiling test. Are we saving 1% of the
computation time ?
is it 10% ?
is it 50% ?
For 1% of computation time savings, we probably shouldn't sacrifice
portability and maintainability...
Thanks
Luis |
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(0009272)
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Nicolas Savoire
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2007-09-24 08:46
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The problem appears on i386 (linux and OSX) platform. Compilation flags and gcc version have no influence on the result.
Test case:
#include <assert.h>
inline int BSplineFloor(double x)
{
#if defined mips || defined sparc || defined __ppc__
return (int)((unsigned int)(x + 2147483648.0) - 2147483648U);
#elif defined i386 || defined _M_IX86
union { unsigned int hilo[2]; double d; } u;
u.d = x + 103079215104.0;
return (int)((u.hilo[1]<<16)|(u.hilo[0]>>16));
#else
return int(floor(x));
#endif
}
int main ()
{
assert(BSplineFloor(0.999999)==0);
} |
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(0009279)
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dbrussak
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2007-09-24 20:35
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Hi,
This particular BSplineFloor() precision issue is the one I reported here in issue 0005692:
http://www.itk.org/Bug/view.php?id=5692 [^]
I'm happy to delete/rescind my issue and just wait for resolution of this one. Is that possible?
Daniel R. |
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(0009942)
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Aviv Hurvitz
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2007-12-16 09:34
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I've also run into the problem where BSplineFloor returns an incorrect result. This caused BSPlineDeformableTransform ::TransformPoint() to SEGFAULT.
Tested on a Pentium 4. Compiled with:
- gcc version 4.1.3 20070629 (prerelease) (Debian 4.1.2-13)
- MS Visual C++ 2005
A sample program:
>>>>>>>>>>>>>>>>>>>>>>>>>
#include <iostream>
#include <math.h>
inline int BSplineFloor(double x)
{
#if defined mips || defined sparc || defined __ppc__
return (int)((unsigned int)(x + 2147483648.0) - 2147483648U);
#elif defined i386 || defined _M_IX86
union { unsigned int hilo[2]; double d; } u;
u.d = x + 103079215104.0;
return (int)((u.hilo[1]<<16)|(u.hilo[0]>>16));
#else
return int(floor(x));
#endif
}
int main(int argc, char *argv[])
{
double x = 16.999995;
int bsplineFloorResult = BSplineFloor(x);
int standardFloor = static_cast<int>( floor(x) );
std::cout.precision(20);
std::cout << "x = " << x << std::endl;
std::cout << "BSspline_floor = " << bsplineFloorResult << std::endl;
std::cout << "Standard floor = " << standardFloor << std::endl;
/* Prints:
x = 16.999994999999998413
BSspline_floor = 17
Standard floor = 16
*/
return 0;
}
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> |
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(0016727)
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Tom Vercauteren
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2009-06-16 04:04
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