bisection.h

/*
    LA: linear algebra C++ interface library
    Copyright (C) 2008 Jiri Pittner <jiri.pittner@jh-inst.cas.cz> or <jiri@pittnerovi.com>

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef _BISECTION_H
#define _BISECTION_H

namespace LA {

//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
}


}//namespace
#endif

LA library home page http://www.pittnerovi.com/la .