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BUG: Fix random number in RGBGibbsPriorFilter::GibbsTotalEnergy #5350

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Merged
thewtex merged 1 commit into from
May 15, 2025
Merged

BUG: Fix random number in RGBGibbsPriorFilter::GibbsTotalEnergy #5350

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2 changes: 1 addition & 1 deletion Modules/Segmentation/MarkovRandomFieldsClassifiers/include/itkRGBGibbsPriorFilter.hxx
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Original file line number Diff line number Diff line change
Expand Up @@ -289,7 +289,7 @@ RGBGibbsPriorFilter<TInputImage, TClassifiedImage>::GibbsTotalEnergy(int i)
if (changeflag)
{
difenergy = energy[label] - energy[1 - label];
const double rand_num{ rand() / 32768.0 };
const double rand_num{ rand() / (RAND_MAX + 1.0) };
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@N-Dekker N-Dekker May 14, 2025 •
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On Windows, using MSVC/Visual Studio 2022, RAND_MAX + 1.0 is exactly 32768.0, but on Linux, using GCC, RAND_MAX + 1.0 may be 2147483648.0.

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@N-Dekker N-Dekker May 15, 2025

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Context of this pull request:

ITK/Modules/Segmentation/MarkovRandomFieldsClassifiers/include/itkRGBGibbsPriorFilter.hxx

Lines 292 to 297 in ab1ba0b

const double rand_num{ rand() / 32768.0 };
double energy_num{ std::exp(static_cast<double>(difenergy * 0.5 * size / (2 * size - m_Temp))) };
if (rand_num < energy_num)
{
m_LabelledImage->SetPixel(offsetIndex3D, 1 - label);
}

So this rand_num is a random threshold for energy_num. On Linux + GCC, the numbers returned by rand() are usually much higher than on Windows + MSVC. So on Linux + GCC, the threshold will be much higher, making it less likely that the if (rand_num < energy_num) clause will be entered.

double energy_num{ std::exp(static_cast<double>(difenergy * 0.5 * size / (2 * size - m_Temp))) };
if (rand_num < energy_num)
{
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