LA_library/bisection.h
2005-09-07 21:47:58 +00:00

63 lines
1.8 KiB
C++

#ifndef _BISECTION_H
#define _BISECTION_H
//general bisection search between dm and hm
//returns dm-1 on failure, otherwise number between dm and hm
//cmp returns 0 on equal, >0 if first > second argument
template<typename INDEX, typename COMPAR, typename SUBJECT>
INDEX bisection_find(INDEX dm, INDEX hm, const SUBJECT *key, const SUBJECT *base , unsigned int lead_dimension_base, COMPAR (*cmp)(const SUBJECT *, const SUBJECT *))
{
if(dm>hm) return(dm-1);
if(dm==hm) return (*cmp)(base+dm*lead_dimension_base,key)? dm-1 :dm;
INDEX sm;
INDEX dm0=dm;
--dm;
++hm;
do
{
sm = (dm+hm)/2;
COMPAR q = (*cmp)(base+sm*lead_dimension_base,key);
if (!q) return(sm);
else if (q<0) dm = sm; else hm = sm;
}
while (hm > dm+1);
return(dm0-1);
}
// interpolation search
//distance is +-0, on its quality the convergence speed depends
template<typename INDEX, typename DISTANCE, typename SUBJECT>
int interpolation_find(INDEX dm0, INDEX high, const SUBJECT *x, const SUBJECT *base , unsigned int lead_dimension_base, DISTANCE (*dist)(const SUBJECT *, const SUBJECT *))
{
INDEX low = dm0;
INDEX mid;
DISTANCE d1,d2,d3,d4;
while(1)
{
d1=(*dist)(x,base+low*lead_dimension_base);
d2=(*dist)(base+high*lead_dimension_base,x);
if(d1<=0 || d2 <=0) break;
d3=(*dist)(base+high*lead_dimension_base,base+low*lead_dimension_base);
mid = low + (int)((d1 * (high-low)) / d3);
if(mid<low||mid>high) laerror("interpolation_find: error in distance function");
d4=(*dist)(x,base+mid*lead_dimension_base);
if(d4>0)
low = mid + 1;
else if(d4<0)
high = mid - 1;
else
return mid;
}
if (d1==0) return low;
if (d2==0) return high;
return dm0-1; // Not found
}
#endif