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sped up Zipf distribution calculation

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joaquintides
2023-06-01 18:39:03 +02:00
parent 2f0db9b81b
commit b6cbc0655e
1 changed files with 37 additions and 9 deletions
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46
zipfian_int_distribution.h
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@@ -60,8 +60,10 @@
* }
*/
/* Joaquin M Lopez Munoz, May 2023: trivial changes to get rid of GCC specific
* functions and some warnings.
/*
* Joaquin M Lopez Munoz, May-Jun 2023:
* - Trivial changes to get rid of GCC specific functions and some warnings.
* - Cached values to speed up zipfian_int_distribution::operator().
*/
#include <cmath>
@@ -84,14 +86,18 @@ public:
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 + 1, __theta)), _M_zeta2theta(zeta(2, __theta)),
_M_alpha(alpha(__theta)), _M_eta(eta(__a, __b, __theta, _M_zeta, _M_zeta2theta)),
_M_1_plus_05_to_theta(_1_plus_05_to_theta(__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(2, __theta)),
_M_alpha(alpha(__theta)), _M_eta(eta(__a, __b, __theta, _M_zeta, _M_zeta2theta)),
_M_1_plus_05_to_theta(_1_plus_05_to_theta(__theta))
{
assert(_M_a <= _M_b && _M_theta > 0.0 && _M_theta < 1.0);
}
@@ -106,6 +112,12 @@ public:
double zeta2theta() const { return _M_zeta2theta; }
double alpha() const { return _M_alpha; }
double eta() const { return _M_eta; }
double _1_plus_05_to_theta() const { return _M_1_plus_05_to_theta; }
friend bool operator==(const param_type& __p1, const param_type& __p2)
{
return __p1._M_a == __p2._M_a
@@ -121,6 +133,9 @@ public:
double _M_theta;
double _M_zeta;
double _M_zeta2theta;
double _M_alpha;
double _M_eta;
double _M_1_plus_05_to_theta;
/**
* @brief Calculates zeta.
@@ -135,6 +150,21 @@ public:
ans += std::pow(1.0/i, __theta);
return ans;
}
double alpha(double __theta)
{
return 1 / (1 - __theta);
};
double eta(_IntType __a, _IntType __b, double __theta, double __zeta, double __zeta2theta)
{
return (1 - std::pow(2.0 / (__b - __a + 1), 1 - __theta)) / (1 - __zeta2theta / __zeta);
}
double _1_plus_05_to_theta(double __theta)
{
return 1.0 + std::pow(0.5, __theta);
}
};
public:
@@ -196,16 +226,14 @@ public:
template<typename _UniformRandomNumberGenerator>
result_type operator()(_UniformRandomNumberGenerator& __urng, const param_type& __p)
{
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;
if(uz < __p._1_plus_05_to_theta()) return __p.a() + 1;
return (result_type)(__p.a() + ((__p.b() - __p.a() + 1) * std::pow(eta*u-eta+1, alpha)));
double ans = (result_type)(__p.a() + ((__p.b() - __p.a() + 1) * std::pow(__p.eta()*u-__p.eta()+1, __p.alpha())));
return ans;
}
/**