1 files changed, 174 insertions, 0 deletions
diff --git a/utils/logval.h b/utils/logval.h
new file mode 100644
index 00000000..37f14ae5
--- /dev/null
+++ b/utils/logval.h
@@ -0,0 +1,174 @@
+#ifndef LOGVAL_H_
+#define LOGVAL_H_
+
+#define LOGVAL_CHECK_NEG false
+
+#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)) {}
+  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) {}
+  static LogVal<T> exp(T lnx) { return LogVal(lnx,false); }
+
+  static LogVal<T> One() { return LogVal(1); }
+  static LogVal<T> Zero() { return LogVal(); }
+  static LogVal<T> e() { return LogVal(1,false); }
+  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(fabs(log(x)),x.s_)
+  friend LogVal abslog(LogVal x) {
+    if (x.v_<0) x.v_=-x.v_;
+    return x;
+  }
+
+  LogVal& 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;
+  }
+
+  void invert() { s_ = !s_; }
+
+  LogVal pow(const T& power) const {
+    LogVal res = *this;
+    res.poweq(power);
+    return res;
+  }
+
+  LogVal root(const T& root) const {
+    return pow(1/root);
+  }
+
+  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) {
+#ifdef LOGVAL_CHECK_NEG
+  if (o.s_) return log(-1.0);
+#endif
+  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