BUG: Fix random number in RGBGibbsPriorFilter::GibbsTotalEnergy
#5350
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The original division of `rand()` by `32768.0` was probably meant to yield a number between `[0, 1>`. However, `rand()` returns an integer between `[0, RAND_MAX]`, and `RAND_MAX` may not be `32767`. In practice, when using GCC, `RAND_MAX` may be as large as `2147483647. The "magic number" `32768.0` was introduced on 12 Jan 2002 already, with commit 074c74f.
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@chentingpc Hi Ting Chen! Could it be that this is originally your code? If so, maybe you can have a look at this pull request! 😃 |
N-Dekker
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May 14, 2025
| { | ||
| 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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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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Context of this pull request:
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.
thewtex
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May 15, 2025
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The original division of
rand()by32768.0was probably meant to yield a number between[0, 1>. However,rand()returns an integer between[0, RAND_MAX], andRAND_MAXmay not be32767. In practice, when using GCC,RAND_MAXmay be as large as2147483647.The "magic number"
32768.0was introduced on 12 Jan 2002 already, with commit 074c74f.