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#ifndef LOGVAL_H_
#define LOGVAL_H_
#define LOGVAL_CHECK_NEG false
#include <boost/functional/hash.hpp>
#include <iostream>
#include <cstdlib>
#include <cmath>
#include <limits>
#include <cassert>
#include "semiring.h"
//TODO: template for supporting negation or not - most uses are for nonnegative "probs" only; probably some 10-20% speedup available
template <class T>
class LogVal {
public:
typedef LogVal<T> Self;
LogVal() : s_(), v_(LOGVAL_LOG0) {}
explicit LogVal(double x) : s_(std::signbit(x)), v_(s_ ? std::log(-x) : std::log(x)) {}
LogVal(init_minus_1) : s_(true),v_(0) { }
LogVal(init_1) : s_(),v_(0) { }
LogVal(init_0) : s_(),v_(LOGVAL_LOG0) { }
LogVal(int x) : s_(x<0), v_(s_ ? std::log(-x) : std::log(x)) {}
LogVal(unsigned x) : s_(0), v_(std::log(x)) { }
LogVal(double lnx,bool sign) : s_(sign),v_(lnx) {}
LogVal(double lnx,init_lnx) : s_(),v_(lnx) {}
static Self exp(T lnx) { return Self(lnx,false); }
// maybe the below are faster than == 1 and == 0. i don't know.
bool is_1() const { return v_==0&&s_==0; }
bool is_0() const { return v_==LOGVAL_LOG0; }
static Self One() { return Self(1); }
static Self Zero() { return Self(); }
static Self e() { return Self(1,false); }
void logeq(const T& v) { s_ = false; v_ = v; }
std::size_t hash_impl() const {
using namespace boost;
return hash_value(v_)+s_;
}
// just like std::signbit, negative means true. weird, i know
bool signbit() const {
return s_;
}
friend inline bool signbit(Self const& x) { return x.signbit(); }
Self& besteq(const Self& a) {
assert(!a.s_ && !s_);
if (a.v_ < v_)
v_=a.v_;
return *this;
}
Self& operator+=(const Self& a) {
if (a.is_0()) 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;
}
Self& operator*=(const Self& a) {
s_ = (s_ != a.s_);
v_ += a.v_;
return *this;
}
Self& operator/=(const Self& a) {
s_ = (s_ != a.s_);
v_ -= a.v_;
return *this;
}
Self& operator-=(const Self& a) {
Self b = a;
b.negate();
return *this += b;
}
// Self(fabs(log(x)),x.s_)
friend Self abslog(Self x) {
if (x.v_<0) x.v_=-x.v_;
return x;
}
Self& poweq(const T& power) {
#if LOGVAL_CHECK_NEG
if (s_) {
std::cerr << "poweq(T) not implemented when s_ is true\n";
std::abort();
} else
#endif
v_ *= power;
return *this;
}
//remember, s_ means negative.
inline bool lt(Self const& o) const {
return s_==o.s_ ? v_ < o.v_ : s_ > o.s_;
}
inline bool gt(Self const& o) const {
return s_==o.s_ ? o.v_ < v_ : s_ < o.s_;
}
Self operator-() const {
return Self(v_,-s_);
}
void negate() { s_ = !s_; }
Self inverse() const { return Self(-v_,s_); }
Self pow(const T& power) const {
Self res = *this;
res.poweq(power);
return res;
}
Self root(const T& root) const {
return pow(1/root);
}
operator T() const {
if (s_) return -std::exp(v_); else return std::exp(v_);
}
T as_float() const {
if (s_) return -std::exp(v_); else return std::exp(v_);
}
bool s_;
T v_;
};
template <class T>
struct semiring_traits<LogVal<T> > : default_semiring_traits<LogVal<T> > {
static const bool has_logplus=true;
static const bool has_besteq=true;
static const bool has_order=true;
static const bool has_subtract=true;
static const bool has_negative=true;
};
// 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<class T>
LogVal<T> operator+(LogVal<T> o1, const LogVal<T>& o2) {
o1 += o2;
return o1;
}
template<class T>
LogVal<T> operator*(LogVal<T> o1, const LogVal<T>& o2) {
o1 *= o2;
return o1;
}
template<class T>
LogVal<T> operator/(LogVal<T> o1, const LogVal<T>& o2) {
o1 /= o2;
return o1;
}
template<class T>
LogVal<T> operator-(LogVal<T> o1, const LogVal<T>& o2) {
o1 -= o2;
return o1;
}
template<class T>
T log(const LogVal<T>& o) {
#ifdef LOGVAL_CHECK_NEG
if (o.s_) return log(-1.0);
#endif
return o.v_;
}
template <class T>
LogVal<T> pow(const LogVal<T>& b, const T& e) {
return b.pow(e);
}
template <class 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 <class T>
bool operator<=(const LogVal<T>& lhs, const LogVal<T>& rhs) {
return (lhs.v_ <= rhs.v_);
}
template <class T>
bool operator>(const LogVal<T>& lhs, const LogVal<T>& rhs) {
return (lhs.v_ > rhs.v_);
}
template <class T>
bool operator>=(const LogVal<T>& lhs, const LogVal<T>& rhs) {
return (lhs.v_ >= rhs.v_);
}
#endif
template <class T>
std::size_t hash_value(const LogVal<T>& x) { return x.hash_impl(); }
template <class T>
bool operator==(const LogVal<T>& lhs, const LogVal<T>& rhs) {
return (lhs.v_ == rhs.v_) && (lhs.s_ == rhs.s_);
}
template <class T>
bool operator!=(const LogVal<T>& lhs, const LogVal<T>& rhs) {
return !(lhs == rhs);
}
#endif
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