<random>: Prevent full-width shifts in independent_bits_engine
#5740
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StephanTLavavej
approved these changes
Sep 25, 2025
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I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed. |
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Thanks for fixing the STL's most common UB mistake! ⏪ 😻 ⏩ |
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Fixes #5719.
The second loop in
operator()is fine because it's only executed if multiple random values are needed (modulo the rejection sampling), i.e.,_Nx > 1. In such cases,_Wx0 <= _Wx / _Nx <= sizeof(_Eres)*8 / 2, so_Wx0+1 < sizeof(_Eres)*8as long as_Eresis more than two bits.