/* -*- mode: c++ -*-
*/
/*
GIFT, a flexible content based image retrieval system.
Copyright (C) 1998, 1999, 2000 CUI, University of Geneva
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 2 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, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#ifndef _MERGE_SORT
#define _MERGE_SORT
#include <algorithm> // using swap
#include <fstream> // file access
/**
A template for merging streams in the sense of mergesort
@params in1,in2 are the streams to be merged
@params out is the stream which contains afterwards the two
merged streams
The stream is considered to contain only elements of type T
This is the principal helper function of merge_sort_streams
*/
template<class T>
void merge_streams(istream& in1, const int inCount1,
istream& in2, const int inCount2,
ostream& out){
{
// cout << "Merging: "
// << inCount1
// << ","
// << inCount2
// << endl;
if(!inCount1){// if there is nothing to merge
for(int i=0;//...copy
i<inCount2;
i++){
T l2;
in2.read(&l2,
sizeof(l2));
assert(in2);
out.write(&l2,
sizeof(l2));
assert(out);
}
return;//and return
}
if(!inCount2){//if there is nothing to merge
for(int i=0;//...copy
i<inCount1;
i++){
T l1;
in1.read(&l1,
sizeof(l1));
assert(in1);
out.write(&l1,
sizeof(l1));
assert(out);
}
return;//and return
}
int lI1(0);
int lI2(0);
//read the first record from both files
T l1;
in1.read(&l1,
sizeof(l1));
assert(in1);
T l2;
in2.read(&l2,
sizeof(l2));
assert(in2);
while((lI1<inCount1)
&&(lI2<inCount2)){
if(l1<l2){
//
out.write(&l1,
sizeof(l1));
assert(out);
//
lI1++;
if(lI1<inCount1){
in1.read(&l1,
sizeof(l1));
assert(in1);
}
}else{
//
out.write(&l2,
sizeof(l2));
//
lI2++;
if(lI2<inCount2){
in2.read(&l2,
sizeof(l2));
assert(in2);
}
}
}
while(lI1<inCount1){
//
out.write(&l1,
sizeof(l1));
//
lI1++;
if(lI1<inCount1){
in1.read(&l1,
sizeof(l1));
assert(in1);
}
}
while(lI2<inCount2){
//
out.write(&l2,
sizeof(l2));
assert(out);
//
lI2++;
if(lI2<inCount2){
in2.read(&l2,
sizeof(l2));
assert(in2);
}
}
}
}
/**
This function sorts a stream containing
elements of type T. The result of the merge sort
is to be found inFileToBeSorted. The temporary file
contains partly sorted garbage of the same size
as the file of name inFileToBeSortedName
@param inFileToBeSortedName the file to be sorted
@param inFileToBeSortedName the name of a temporary file
*/
template<class T>
void merge_sort_streams(const char* inFileToBeSortedName,
const char* inTemporaryName){
const char* lFileToBeSortedName(inFileToBeSortedName);
const char* lTemporaryName(inTemporaryName);
int lFileSize(0);
ifstream lToBeSorted1(inFileToBeSortedName);
lToBeSorted1.seekg(0,
ios::end);
lFileSize=lToBeSorted1.tellg();
lToBeSorted1.close();
ofstream lTemporary;
ifstream lToBeSorted2;
int lCount(0);
for(int iMergeSize=sizeof(T);
(iMergeSize < lFileSize)
|| (lCount%2)
// ||(lCount%2) makes sure that we will get
// the result in inFileToBeSorted
;
iMergeSize <<= 1,lCount++){
cout << "MERGESORT MergeSize "
<< iMergeSize
<< endl;
lToBeSorted1.open(lFileToBeSortedName);
lToBeSorted1.clear();
lToBeSorted2.open(lFileToBeSortedName);
lToBeSorted2.clear();
lTemporary.open(lTemporaryName);
lTemporary.clear();
for(int i=0;
i<lFileSize;
i += iMergeSize*2){
lToBeSorted1.seekg(i);
assert(lToBeSorted1);
if(i+iMergeSize<lFileSize){
lToBeSorted2.seekg(i+iMergeSize);
assert(lToBeSorted2);
}
int lMergeSize1=lFileSize-i;
int lMergeSize2=lFileSize-i-iMergeSize;
// lToBeSorted1.clear();
// lToBeSorted2.clear();
if(lMergeSize1>iMergeSize){
lMergeSize1=iMergeSize;
}
if(lMergeSize2>iMergeSize){
lMergeSize2=iMergeSize;
}
if(lMergeSize1<0){
lMergeSize1=0;
}
if(lMergeSize2<0){
lMergeSize2=0;
}
merge_streams<T>(lToBeSorted1,
lMergeSize1/sizeof(T),
lToBeSorted2,
lMergeSize2/sizeof(T),
lTemporary);
}
lTemporary.close();
lToBeSorted1.close();
lToBeSorted2.close();
swap(lFileToBeSortedName,
lTemporaryName);
}
}
#endif
Documentation generated by muellerw@pc7170 on Son Okt 8 16:04:40 CEST 2000