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random.tcc: binomial_distribution: mitigate undocumented behaviour #79

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random.tcc: binomial_distribution: mitigate undocumented behaviour #79

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2 changes: 1 addition & 1 deletion libstdc++-v3/include/bits/random.tcc
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Original file line number Diff line number Diff line change
Expand Up @@ -1500,7 +1500,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// sqrt(pi / 2)
const double __spi_2 = 1.2533141373155002512078826424055226L;
_M_s1 = std::sqrt(__np * __1p) * (1 + _M_d1 / (4 * __np));
_M_s2 = std::sqrt(__np * __1p) * (1 + _M_d2 / (4 * _M_t * __1p));
_M_s2 = std::sqrt(__np * __1p) * (1 + _M_d2 / (4. * _M_t * __1p));
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@Pignotto Pignotto Jan 21, 2023 •
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In particular, for values of _M_t that overflow to 0 by the 4* multiplication, the operator()(_UniformRandomNumberGenerator& __urng, const param_type& __param) hangs in an infinite loop as noted and described on https://stackoverflow.com/q/75179395/15114624

_M_c = 2 * _M_d1 / __np;
_M_a1 = std::exp(_M_c) * _M_s1 * __spi_2;
const double __a12 = _M_a1 + _M_s2 * __spi_2;
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