// Test of closest pair algorithms
// David Eppstein, UC Irvine, 19 Apr 1997
//
// Programmer interface for points and distances

#ifndef DISTANCES_H
#define DISTANCES_H

#include <float.h>

// a special flag value for distances, larger than any other possible distance
// value. ClosestPairs are allowed to ignore pairs at this distance apart
// (and produce an error rather than return a pair at this distance).
//
#define MAX_DISTANCE DBL_MAX

// All points are black boxes to us, interpreted only by the distance fn.
// We represent them as integers rather than e.g. void *, so that our
// data structures can use them as array indices without e.g. having
// to go through an extra layer of hashing.
//
typedef unsigned long point;

// For instrumentation purposes, we keep track of the
// number of times a distance function is called throughout the program.
//
extern unsigned long gDistances;

// Distance function object.
//
// A distance function is defined to be something that takes a pair of
// point arguments and returns a (floating point) distance.
// We assume distances are symmetric (d(a,b)=d(b,a)) but do not require
// the triangle inequality, nonnegativity, or other assumptions.
//
// This is a class rather than a function so it can keep track of any
// global information necessary to interpret the point arguments it is given.
//
class Distance {
 public:
	virtual double operator () (point, point) { gDistances++; return 0.0; }
};

#endif