TableLookup.h

#ifndef TableLookup_h__
#define TableLookup_h__
 
#include <cstddef>
#include <functional>
#include <string>
#include <utility>
#include <vector>
 
namespace Ship
{
 
class WarnOnce
{
public:
   using Sink = std::function<void(const std::string&)>;
 
   void SetSink(Sink sink) { m_sink = std::move(sink); }
 
   void Warn(const std::string& message)
   {
      if (m_count++ == 0 && m_sink) {
         m_sink(message);
      }
   }
 
   int Count() const { return m_count; }
 
private:
   Sink m_sink;
   int  m_count = 0;
};
 
struct AxisInterval
{
   std::size_t lower;   
   double      value;   
   bool        held;    
};
 
inline AxisInterval FindInterval(const std::vector<double>& axis, double x)
{
   if (axis.size() < 2) {
      return {0, axis.empty() ? x : axis.front(), axis.empty() || x != axis.front()};
   }
   if (!(x >= axis.front())) {   // also holds a NaN to the first node
      return {0, axis.front(), true};
   }
   if (x > axis.back()) {
      return {axis.size() - 2, axis.back(), true};
   }
   std::size_t lower = 0;
   while (lower + 2 < axis.size() && axis[lower + 1] < x) {
      ++lower;
   }
   return {lower, x, false};
}
 
inline double Lerp(double xLow, double xHigh, double yLow, double yHigh, double x)
{
   if (xHigh == xLow) {
      return yLow;
   }
   return yLow + (yHigh - yLow) * (x - xLow) / (xHigh - xLow);
}
 
}   // namespace Ship
 
#endif   // TableLookup_h__