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Fix integer overflow #2

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Fix integer overflow #2

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26 changes: 17 additions & 9 deletions zipfian_int_distribution.h
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Original file line number Diff line number Diff line change
Expand Up @@ -30,7 +30,7 @@
/*
* The zipfian_int_distribution class is intended to be compatible with other
* distributions introduced in #include <random> by the C++11 standard.
*
*
* Usage example:
* #include <random>
* #include "zipfian_int_distribution.h"
Expand All @@ -47,7 +47,7 @@
* value which becomes prohibetively expensive for very large ranges. As an
* alternative for such cases, the user can pass the pre-calculated values and
* avoid the calculation every time.
*
*
* Usage example:
* #include <random>
* #include "zipfian_int_distribution.h"
Expand Down Expand Up @@ -80,14 +80,14 @@ class zipfian_int_distribution

explicit param_type(_IntType __a = 0, _IntType __b = std::numeric_limits<_IntType>::max(), double __theta = 0.99)
: _M_a(__a), _M_b(__b), _M_theta(__theta),
_M_zeta(zeta(_M_b - _M_a + 1, __theta)), _M_zeta2theta(zeta(2, __theta))
_M_zeta(zeta(_M_b - _M_a, __theta)), _M_zeta2theta(zeta(2, __theta))
{
assert(_M_a <= _M_b && _M_theta > 0.0 && _M_theta < 1.0);
}

explicit param_type(_IntType __a, _IntType __b, double __theta, double __zeta)
: _M_a(__a), _M_b(__b), _M_theta(__theta), _M_zeta(__zeta),
_M_zeta2theta(zeta(2, __theta))
_M_zeta2theta(zeta(1, __theta))
{
__glibcxx_assert(_M_a <= _M_b && _M_theta > 0.0 && _M_theta < 1.0);
}
Expand Down Expand Up @@ -124,11 +124,19 @@ class zipfian_int_distribution
* @param __n [IN] The size of the domain.
* @param __theta [IN] The skew factor of the distribution.
*/
double zeta(unsigned long __n, double __theta)
double zeta(unsigned long __n_minus_1, double __theta)
{
double ans = 0.0;
for(unsigned long i=1; i<=__n; ++i)
unsigned long max = std::numeric_limits<unsigned long>::max() >> (64 - std::numeric_limits<double>::digits);
unsigned long end = std::min(__n_minus_1, max) + 1;
for(unsigned long i=1; i<=end; ++i)
ans += std::pow(1.0/i, __theta);
if (end <= __n_minus_1) {
long double lf_i = static_cast<long double>(end) + 1, lf_theta = __theta, lf_ans = 0.0;
for (unsigned long i=end-1; i<__n_minus_1; lf_i+=1, ++i)
lf_ans += std::pow(1.0/lf_i, lf_theta);
ans += static_cast<double>(lf_ans);
}
return ans;
}
};
Expand Down Expand Up @@ -194,9 +202,9 @@ class zipfian_int_distribution
{
double alpha = 1 / (1 - __p.theta());
double eta = (1 - std::pow(2.0 / (__p.b() - __p.a() + 1), 1 - __p.theta())) / (1 - __p.zeta2theta() / __p.zeta());

double u = std::generate_canonical<double, std::numeric_limits<double>::digits, _UniformRandomNumberGenerator>(__urng);

double uz = u * __p.zeta();
if(uz < 1.0) return __p.a();
if(uz < 1.0 + std::pow(0.5, __p.theta())) return __p.a() + 1;
Expand Down