/*
 *  Average fields:
 *
 *  This program averages n input files and outputs the result.  It
 *  assumes that the inputs are all in single-precision IEEE-BE ("big
 *  endian") format.  Internally, the averaging is done in IEEE double
 *  precision and the final result is converted back into IEEE-BE
 *  immediately before being written.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>

#include <iostream>
#include <fstream>
#include <string>

#define uint32  unsigned int

#define BUF_SIZE 65536
#define htonl(A)  ((((uint32)(A) & 0xff000000) >> 24) | \
                   (((uint32)(A) & 0x00ff0000) >> 8)  | \
                   (((uint32)(A) & 0x0000ff00) << 8)  | \
                   (((uint32)(A) & 0x000000ff) << 24))
#define bswap32(A)  ( ((uint32)(A) >> 24) | \
                      (((uint32)(A) & 0x00ff0000) >> 8) | \
                      (((uint32)(A) & 0x0000ff00) << 8) | \
                      ((uint32)(A) << 24) )

int
main( int argc, char** argv )
{
    char buff[BUF_SIZE];
    int i;
    int nbytes;
    using namespace std;
    struct stat st;
    void * vptr;
    double * dptr;
    float * fptr;
    uint32 u32;

    if (argc < 4) {
	cerr << "\nError: at least three file names must be supplied." << endl;
	exit(1);
    }

    string fname(argv[1]);
    stat(fname.c_str(), &st);
    nbytes = st.st_size;
    cout << "The file \"" << fname 
	 << "\" has size: " << nbytes << " bytes" << endl;
    int ndouble = nbytes/4;

    dptr = new double[ndouble];
    if (dptr == NULL) {
	cerr << "\nError: unable to allocate sufficient memory." << endl;
	exit(1);
    }
    for (int j=0; j<ndouble; j++) {
	dptr[j] = 0.0;
    }

    for (i=1; i<(argc-1); i++) {
	cout << "  arg " << i << " is " << argv[i] << endl;

	stat(argv[i], &st);
	if (st.st_size != nbytes) {
	    cerr << "\nError: files size does not agree for file \"" 
		 << argv[i] << "\"." << endl;
	    exit(1);
	}
	int fd;
	if ((fd = open(argv[i], O_RDONLY)) == -1) {
	    cerr << "\nError: can't open() file \"" << argv[i] << "\"." << endl;
	    exit(1);
	}
	vptr = mmap( (void *)0, (size_t)(nbytes), 
		     PROT_READ, MAP_PRIVATE, fd, 0 );
	if (vptr == NULL) {
	    cerr << "\nError: can't mmap() the file \"" << argv[i] << "\"." << endl;
	    exit(1);
 	}

	//  Average the fields
	unsigned int * uip = (unsigned int *)(vptr);
	for (int j=0; j<ndouble; j++) {
	    u32 = *uip;
	    unsigned int i32s = bswap32(u32);
	    float flt = *((float *)(&i32s));
	    //  cout << "   flt = " << flt << endl;
	    dptr[j] += double(flt);
	    uip++;
	}

	munmap(vptr, (size_t)(nbytes));
    }

    double denom = 1.0/double(argc - 2);
    fptr = new float[ndouble];
    for (int j=0; j<ndouble; j++) {
	float flt = (float(denom * dptr[j]));
	unsigned int i32s = bswap32(*((unsigned int *)(&flt)));
	fptr[j] = *((float *)(&i32s));
    }
    i = argc - 1;
    int fdo;
    if ((fdo = open(argv[i], (O_CREAT | O_WRONLY), 
		    (S_IRUSR | S_IWUSR))) == -1) {
	cerr << "\nError: can't open() file \"" << argv[i] << "\"." << endl;
	    exit(1);
    }
    char * aptr = (char *)(fptr);
    size_t inc_bytes_out;
    size_t tot_bytes_out = 0;
    bool write_needed = true;
    while (write_needed) {
	inc_bytes_out = write(fdo, (void *)(aptr + tot_bytes_out), 
			       (size_t)(nbytes - tot_bytes_out));
	tot_bytes_out += inc_bytes_out;
	if ((inc_bytes_out == 0) && (fdo != -1))
	    write_needed = false;
    }

    delete[] dptr;
    delete[] fptr;
    return 0;
}