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#ifndef LOGVAL_H_
#define LOGVAL_H_
#include <iostream>
#include <cstdlib>
#include <cmath>
#include <limits>
template <typename T>
class LogVal {
public:
LogVal() : s_(), v_(-std::numeric_limits<T>::infinity()) {}
explicit LogVal(double x) : s_(std::signbit(x)), v_(s_ ? std::log(-x) : std::log(x)) {}
static LogVal<T> One() { return LogVal(1); }
static LogVal<T> Zero() { return LogVal(); }
void logeq(const T& v) { s_ = false; v_ = v; }
LogVal& operator+=(const LogVal& a) {
if (a.v_ == -std::numeric_limits<T>::infinity()) return *this;
if (a.s_ == s_) {
if (a.v_ < v_) {
v_ = v_ + log1p(std::exp(a.v_ - v_));
} else {
v_ = a.v_ + log1p(std::exp(v_ - a.v_));
}
} else {
if (a.v_ < v_) {
v_ = v_ + log1p(-std::exp(a.v_ - v_));
} else {
v_ = a.v_ + log1p(-std::exp(v_ - a.v_));
s_ = !s_;
}
}
return *this;
}
LogVal& operator*=(const LogVal& a) {
s_ = (s_ != a.s_);
v_ += a.v_;
return *this;
}
LogVal& operator/=(const LogVal& a) {
s_ = (s_ != a.s_);
v_ -= a.v_;
return *this;
}
LogVal& operator-=(const LogVal& a) {
LogVal b = a;
b.invert();
return *this += b;
}
LogVal& poweq(const T& power) {
if (s_) {
std::cerr << "poweq(T) not implemented when s_ is true\n";
std::abort();
} else {
v_ *= power;
}
return *this;
}
void invert() { s_ = !s_; }
LogVal pow(const T& power) const {
LogVal res = *this;
res.poweq(power);
return res;
}
operator T() const {
if (s_) return -std::exp(v_); else return std::exp(v_);
}
bool s_;
T v_;
};
// copy elision - as opposed to explicit copy of LogVal<T> const& o1, we should be able to construct Logval r=a+(b+c) as a single result in place in r. todo: return std::move(o1) - C++0x
template<typename T>
LogVal<T> operator+(LogVal<T> o1, const LogVal<T>& o2) {
o1 += o2;
return o1;
}
template<typename T>
LogVal<T> operator*(LogVal<T> o1, const LogVal<T>& o2) {
o1 *= o2;
return o1;
}
template<typename T>
LogVal<T> operator/(LogVal<T> o1, const LogVal<T>& o2) {
o1 /= o2;
return o1;
}
template<typename T>
LogVal<T> operator-(LogVal<T> o1, const LogVal<T>& o2) {
o1 -= o2;
return o1;
}
template<typename T>
T log(const LogVal<T>& o) {
if (o.s_) return log(-1.0);
return o.v_;
}
template <typename T>
LogVal<T> pow(const LogVal<T>& b, const T& e) {
return b.pow(e);
}
template <typename T>
bool operator<(const LogVal<T>& lhs, const LogVal<T>& rhs) {
if (lhs.s_ == rhs.s_) {
return (lhs.v_ < rhs.v_);
} else {
return lhs.s_ > rhs.s_;
}
}
#if 0
template <typename T>
bool operator<=(const LogVal<T>& lhs, const LogVal<T>& rhs) {
return (lhs.v_ <= rhs.v_);
}
template <typename T>
bool operator>(const LogVal<T>& lhs, const LogVal<T>& rhs) {
return (lhs.v_ > rhs.v_);
}
template <typename T>
bool operator>=(const LogVal<T>& lhs, const LogVal<T>& rhs) {
return (lhs.v_ >= rhs.v_);
}
#endif
template <typename T>
bool operator==(const LogVal<T>& lhs, const LogVal<T>& rhs) {
return (lhs.v_ == rhs.v_) && (lhs.s_ == rhs.s_);
}
template <typename T>
bool operator!=(const LogVal<T>& lhs, const LogVal<T>& rhs) {
return !(lhs == rhs);
}
#endif
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